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 $41.44   12.693%   $46.7   $46.70   $46.70   $46.70  
  Purchase #2 $235.34   10.834%   $260.8367   $260.84   $260.85   $260.80  
  Purchase #3 $222.41   12.412%   $250.0155   $250.02   $250.00   $250.00  
  Purchase #4 $26.65   7.745%   $28.714   $28.71   $28.70   $28.70  
  Purchase #5 $167.95   9.726%   $184.2848   $184.28   $184.30   $184.30  
  Purchase #6 $127.93   6.758%   $136.5755   $136.58   $136.60   $136.60  
  Purchase #7 $47.67   12.498%   $53.6278   $53.63   $53.65   $53.60  
  7 purchase totals = $869.39       $960.7543   $960.76   $960.80   $960.70