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 $156.60   8.269%   $169.5493   $169.55   $169.55   $169.50  
  Purchase #2 $122.86   11.187%   $136.6043   $136.60   $136.60   $136.60  
  Purchase #3 $205.40   10.685%   $227.347   $227.35   $227.35   $227.30  
  Purchase #4 $46.75   12.764%   $52.7172   $52.72   $52.70   $52.70  
  Purchase #5 $234.33   7.611%   $252.1649   $252.16   $252.15   $252.20  
  Purchase #6 $34.96   4.334%   $36.4752   $36.48   $36.50   $36.50  
  Purchase #7 $168.92   9.852%   $185.562   $185.56   $185.55   $185.60  
  7 purchase totals = $969.82       $1,060.4199   $1,060.42   $1,060.40   $1,060.40