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 $116.35   13.499%   $132.0561   $132.06   $132.05   $132.10  
  Purchase #2 $173.67   13.394%   $196.9314   $196.93   $196.95   $196.90  
  Purchase #3 $217.93   12.866%   $245.9689   $245.97   $245.95   $246.00  
  Purchase #4 $14.80   3.330%   $15.2928   $15.29   $15.30   $15.30  
  Purchase #5 $166.88   4.871%   $175.0087   $175.01   $175.00   $175.00  
  Purchase #6 $66.65   3.470%   $68.9628   $68.96   $68.95   $69.00  
  Purchase #7 $159.86   10.349%   $176.4039   $176.40   $176.40   $176.40  
  7 purchase totals = $916.14       $1,010.6246   $1,010.62   $1,010.60   $1,010.70