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 $58.88   8.133%   $63.6687   $63.67   $63.65   $63.70  
  Purchase #2 $34.39   4.250%   $35.8516   $35.85   $35.85   $35.90  
  Purchase #3 $96.97   5.388%   $102.1947   $102.19   $102.20   $102.20  
  Purchase #4 $214.35   5.367%   $225.8542   $225.85   $225.85   $225.90  
  Purchase #5 $90.71   11.824%   $101.4356   $101.44   $101.45   $101.40  
  Purchase #6 $143.84   4.389%   $150.1531   $150.15   $150.15   $150.20  
  Purchase #7 $108.50   9.673%   $118.9952   $119.00   $119.00   $119.00  
  7 purchase totals = $747.64       $798.1531   $798.15   $798.15   $798.30