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 $177.78   13.508%   $201.7945   $201.79   $201.80   $201.80  
  Purchase #2 $174.95   11.207%   $194.5566   $194.56   $194.55   $194.60  
  Purchase #3 $105.39   11.481%   $117.4898   $117.49   $117.50   $117.50  
  Purchase #4 $149.41   8.484%   $162.0859   $162.09   $162.10   $162.10  
  Purchase #5 $33.31   5.349%   $35.0918   $35.09   $35.10   $35.10  
  Purchase #6 $42.30   6.866%   $45.2043   $45.20   $45.20   $45.20  
  Purchase #7 $23.87   9.226%   $26.0722   $26.07   $26.05   $26.10  
  7 purchase totals = $707.01       $782.2951   $782.29   $782.30   $782.40