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 $250.89   9.716%   $275.2665   $275.27   $275.25   $275.30  
  Purchase #2 $118.43   12.322%   $133.0229   $133.02   $133.00   $133.00  
  Purchase #3 $239.63   8.843%   $260.8205   $260.82   $260.80   $260.80  
  Purchase #4 $192.52   10.413%   $212.5671   $212.57   $212.55   $212.60  
  Purchase #5 $47.69   3.628%   $49.4202   $49.42   $49.40   $49.40  
  Purchase #6 $37.93   3.556%   $39.2788   $39.28   $39.30   $39.30  
  Purchase #7 $135.84   3.616%   $140.752   $140.75   $140.75   $140.80  
  7 purchase totals = $1,022.93       $1,111.1280   $1,111.13   $1,111.05   $1,111.20