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 $64.92   3.121%   $66.9462   $66.95   $66.95   $66.90  
  Purchase #2 $75.46   12.111%   $84.599   $84.60   $84.60   $84.60  
  Purchase #3 $189.51   12.697%   $213.5721   $213.57   $213.55   $213.60  
  Purchase #4 $221.41   9.511%   $242.4683   $242.47   $242.45   $242.50  
  Purchase #5 $167.88   3.250%   $173.3361   $173.34   $173.35   $173.30  
  Purchase #6 $73.73   11.379%   $82.1197   $82.12   $82.10   $82.10  
  Purchase #7 $153.85   3.232%   $158.8224   $158.82   $158.80   $158.80  
  7 purchase totals = $946.76       $1,021.8638   $1,021.87   $1,021.80   $1,021.80