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 $62.98   3.236%   $65.018   $65.02   $65.00   $65.00  
  Purchase #2 $45.99   12.631%   $51.799   $51.80   $51.80   $51.80  
  Purchase #3 $181.75   10.315%   $200.4975   $200.50   $200.50   $200.50  
  Purchase #4 $203.86   4.764%   $213.5719   $213.57   $213.55   $213.60  
  Purchase #5 $156.62   7.589%   $168.5059   $168.51   $168.50   $168.50  
  Purchase #6 $89.63   6.146%   $95.1387   $95.14   $95.15   $95.10  
  Purchase #7 $138.59   4.348%   $144.6159   $144.62   $144.60   $144.60  
  7 purchase totals = $879.42       $939.1469   $939.16   $939.10   $939.10