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 $84.98   12.195%   $95.3433   $95.34   $95.35   $95.30  
  Purchase #2 $188.83   11.221%   $210.0186   $210.02   $210.00   $210.00  
  Purchase #3 $222.84   12.549%   $250.8042   $250.80   $250.80   $250.80  
  Purchase #4 $56.83   11.391%   $63.3035   $63.30   $63.30   $63.30  
  Purchase #5 $53.58   3.276%   $55.3353   $55.34   $55.35   $55.30  
  Purchase #6 $90.61   8.745%   $98.5338   $98.53   $98.55   $98.50  
  Purchase #7 $47.79   8.761%   $51.9769   $51.98   $52.00   $52.00  
  7 purchase totals = $745.46       $825.3156   $825.31   $825.35   $825.20