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 $33.27   6.329%   $35.3757   $35.38   $35.40   $35.40  
  Purchase #2 $125.55   12.802%   $141.6229   $141.62   $141.60   $141.60  
  Purchase #3 $195.51   7.752%   $210.6659   $210.67   $210.65   $210.70  
  Purchase #4 $153.27   7.237%   $164.3621   $164.36   $164.35   $164.40  
  Purchase #5 $218.74   13.521%   $248.3158   $248.32   $248.30   $248.30  
  Purchase #6 $93.72   3.517%   $97.0161   $97.02   $97.00   $97.00  
  Purchase #7 $122.45   5.717%   $129.4505   $129.45   $129.45   $129.50  
  7 purchase totals = $942.51       $1,026.8090   $1,026.82   $1,026.75   $1,026.90