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 $56.55   12.148%   $63.4197   $63.42   $63.40   $63.40  
  Purchase #2 $208.43   3.275%   $215.2561   $215.26   $215.25   $215.30  
  Purchase #3 $18.27   4.127%   $19.024   $19.02   $19.00   $19.00  
  Purchase #4 $37.25   4.294%   $38.8495   $38.85   $38.85   $38.80  
  Purchase #5 $203.54   7.536%   $218.8788   $218.88   $218.90   $218.90  
  Purchase #6 $165.73   10.485%   $183.1068   $183.11   $183.10   $183.10  
  Purchase #7 $22.49   6.823%   $24.0245   $24.02   $24.00   $24.00  
  7 purchase totals = $712.26       $762.5594   $762.56   $762.50   $762.50