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 $123.93   8.361%   $134.2918   $134.29   $134.30   $134.30  
  Purchase #2 $94.26   10.303%   $103.9716   $103.97   $103.95   $104.00  
  Purchase #3 $31.48   3.380%   $32.544   $32.54   $32.55   $32.50  
  Purchase #4 $25.86   7.582%   $27.8207   $27.82   $27.80   $27.80  
  Purchase #5 $91.45   10.833%   $101.3568   $101.36   $101.35   $101.40  
  Purchase #6 $200.61   5.614%   $211.8722   $211.87   $211.85   $211.90  
  Purchase #7 $109.71   9.643%   $120.2893   $120.29   $120.30   $120.30  
  7 purchase totals = $677.30       $732.1464   $732.14   $732.10   $732.20