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 $31.96   13.810%   $36.3737   $36.37   $36.35   $36.40  
  Purchase #2 $134.39   12.142%   $150.7076   $150.71   $150.70   $150.70  
  Purchase #3 $192.54   10.205%   $212.1887   $212.19   $212.20   $212.20  
  Purchase #4 $223.39   5.863%   $236.4874   $236.49   $236.50   $236.50  
  Purchase #5 $232.99   12.361%   $261.7899   $261.79   $261.80   $261.80  
  Purchase #6 $110.80   11.343%   $123.368   $123.37   $123.35   $123.40  
  Purchase #7 $29.74   4.263%   $31.0078   $31.01   $31.00   $31.00  
  7 purchase totals = $955.81       $1,051.9231   $1,051.93   $1,051.90   $1,052.00