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 $68.41   9.726%   $75.0636   $75.06   $75.05   $75.10  
  Purchase #2 $213.50   12.114%   $239.3634   $239.36   $239.35   $239.40  
  Purchase #3 $203.39   12.166%   $228.1344   $228.13   $228.15   $228.10  
  Purchase #4 $5.47   8.160%   $5.9164   $5.92   $5.90   $5.90  
  Purchase #5 $185.71   7.613%   $199.8481   $199.85   $199.85   $199.80  
  Purchase #6 $177.45   5.112%   $186.5212   $186.52   $186.50   $186.50  
  Purchase #7 $130.60   9.531%   $143.0475   $143.05   $143.05   $143.00  
  7 purchase totals = $984.53       $1,077.8946   $1,077.89   $1,077.85   $1,077.80