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 $63.61   7.635%   $68.4666   $68.47   $68.45   $68.50  
  Purchase #2 $224.62   10.182%   $247.4908   $247.49   $247.50   $247.50  
  Purchase #3 $185.78   12.162%   $208.3746   $208.37   $208.35   $208.40  
  Purchase #4 $178.27   13.169%   $201.7464   $201.75   $201.75   $201.70  
  Purchase #5 $85.71   12.357%   $96.3012   $96.30   $96.30   $96.30  
  Purchase #6 $69.71   3.530%   $72.1708   $72.17   $72.15   $72.20  
  Purchase #7 $49.78   8.570%   $54.0461   $54.05   $54.05   $54.00  
  7 purchase totals = $857.48       $948.5965   $948.60   $948.55   $948.60