Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $119.92   8.281%   $129.8506   $129.85   $129.85   $129.90  
  Purchase #2 $201.67   12.675%   $227.2317   $227.23   $227.25   $227.20  
  Purchase #3 $160.54   12.492%   $180.5947   $180.59   $180.60   $180.60  
  Purchase #4 $238.64   9.316%   $260.8717   $260.87   $260.85   $260.90  
  Purchase #5 $242.68   13.869%   $276.3373   $276.34   $276.35   $276.30  
  Purchase #6 $113.58   4.204%   $118.3549   $118.35   $118.35   $118.40  
  Purchase #7 $154.49   12.771%   $174.2199   $174.22   $174.20   $174.20  
  7 purchase totals = $1,231.52       $1,367.4608   $1,367.45   $1,367.45   $1,367.50