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 $58.97   8.398%   $63.9223   $63.92   $63.90   $63.90  
  Purchase #2 $113.92   3.498%   $117.9049   $117.90   $117.90   $117.90  
  Purchase #3 $211.54   3.813%   $219.606   $219.61   $219.60   $219.60  
  Purchase #4 $59.62   9.858%   $65.4973   $65.50   $65.50   $65.50  
  Purchase #5 $86.41   7.118%   $92.5607   $92.56   $92.55   $92.60  
  Purchase #6 $184.80   3.270%   $190.843   $190.84   $190.85   $190.80  
  Purchase #7 $123.38   8.435%   $133.7871   $133.79   $133.80   $133.80  
  7 purchase totals = $838.64       $884.1213   $884.12   $884.10   $884.10