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 $32.46   3.761%   $33.6808   $33.68   $33.70   $33.70  
  Purchase #2 $175.74   10.525%   $194.2366   $194.24   $194.25   $194.20  
  Purchase #3 $162.43   13.524%   $184.397   $184.40   $184.40   $184.40  
  Purchase #4 $37.45   13.470%   $42.4945   $42.49   $42.50   $42.50  
  Purchase #5 $230.97   10.749%   $255.797   $255.80   $255.80   $255.80  
  Purchase #6 $70.71   11.646%   $78.9449   $78.94   $78.95   $78.90  
  Purchase #7 $22.97   8.622%   $24.9505   $24.95   $24.95   $25.00  
  7 purchase totals = $732.73       $814.5013   $814.50   $814.55   $814.50