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 $93.73   9.407%   $102.5472   $102.55   $102.55   $102.50  
  Purchase #2 $180.84   8.151%   $195.5803   $195.58   $195.60   $195.60  
  Purchase #3 $14.67   5.835%   $15.526   $15.53   $15.55   $15.50  
  Purchase #4 $96.45   5.216%   $101.4808   $101.48   $101.50   $101.50  
  Purchase #5 $65.70   13.318%   $74.4499   $74.45   $74.45   $74.40  
  Purchase #6 $136.90   11.703%   $152.9214   $152.92   $152.90   $152.90  
  Purchase #7 $204.67   13.790%   $232.894   $232.89   $232.90   $232.90  
  7 purchase totals = $792.96       $875.3996   $875.40   $875.45   $875.30