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 $22.94   11.714%   $25.6272   $25.63   $25.65   $25.60  
  Purchase #2 $222.79   6.215%   $236.6364   $236.64   $236.65   $236.60  
  Purchase #3 $148.45   8.818%   $161.5403   $161.54   $161.55   $161.50  
  Purchase #4 $155.38   8.188%   $168.1025   $168.10   $168.10   $168.10  
  Purchase #5 $130.45   4.134%   $135.8428   $135.84   $135.85   $135.80  
  Purchase #6 $28.32   11.503%   $31.5776   $31.58   $31.60   $31.60  
  Purchase #7 $44.37   6.649%   $47.3202   $47.32   $47.30   $47.30  
  7 purchase totals = $752.70       $806.6470   $806.65   $806.70   $806.50