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 $125.26   7.458%   $134.6019   $134.60   $134.60   $134.60  
  Purchase #2 $93.34   8.173%   $100.9687   $100.97   $100.95   $101.00  
  Purchase #3 $188.73   5.689%   $199.4668   $199.47   $199.45   $199.50  
  Purchase #4 $24.73   4.735%   $25.901   $25.90   $25.90   $25.90  
  Purchase #5 $6.57   9.163%   $7.172   $7.17   $7.15   $7.20  
  Purchase #6 $24.30   6.475%   $25.8734   $25.87   $25.85   $25.90  
  Purchase #7 $28.83   11.340%   $32.0993   $32.10   $32.10   $32.10  
  7 purchase totals = $491.76       $526.0831   $526.08   $526.00   $526.20