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 $211.59   10.811%   $234.465   $234.47   $234.45   $234.50  
  Purchase #2 $58.60   13.542%   $66.5356   $66.54   $66.55   $66.50  
  Purchase #3 $177.89   13.551%   $201.9959   $202.00   $202.00   $202.00  
  Purchase #4 $245.71   10.707%   $272.0182   $272.02   $272.00   $272.00  
  Purchase #5 $93.84   9.504%   $102.7586   $102.76   $102.75   $102.80  
  Purchase #6 $184.45   4.839%   $193.3755   $193.38   $193.40   $193.40  
  Purchase #7 $214.36   10.556%   $236.9878   $236.99   $237.00   $237.00  
  7 purchase totals = $1,186.44       $1,308.1366   $1,308.16   $1,308.15   $1,308.20