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 $87.43   7.115%   $93.6506   $93.65   $93.65   $93.70  
  Purchase #2 $53.34   3.801%   $55.3675   $55.37   $55.35   $55.40  
  Purchase #3 $46.72   6.633%   $49.8189   $49.82   $49.80   $49.80  
  Purchase #4 $84.58   12.569%   $95.2109   $95.21   $95.20   $95.20  
  Purchase #5 $143.99   4.176%   $150.003   $150.00   $150.00   $150.00  
  Purchase #6 $46.38   10.448%   $51.2258   $51.23   $51.25   $51.20  
  Purchase #7 $221.80   8.761%   $241.2319   $241.23   $241.25   $241.20  
  7 purchase totals = $684.24       $736.5086   $736.51   $736.50   $736.50