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 $48.62   12.503%   $54.699   $54.70   $54.70   $54.70  
  Purchase #2 $153.62   9.597%   $168.3629   $168.36   $168.35   $168.40  
  Purchase #3 $141.43   12.269%   $158.782   $158.78   $158.80   $158.80  
  Purchase #4 $232.31   6.257%   $246.8456   $246.85   $246.85   $246.80  
  Purchase #5 $144.68   5.450%   $152.5651   $152.57   $152.55   $152.60  
  Purchase #6 $14.59   5.637%   $15.4124   $15.41   $15.40   $15.40  
  Purchase #7 $144.48   10.722%   $159.9711   $159.97   $159.95   $160.00  
  7 purchase totals = $879.73       $956.6381   $956.64   $956.60   $956.70