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 $218.29   11.861%   $244.1814   $244.18   $244.20   $244.20  
  Purchase #2 $60.26   6.861%   $64.3944   $64.39   $64.40   $64.40  
  Purchase #3 $126.28   4.638%   $132.1369   $132.14   $132.15   $132.10  
  Purchase #4 $152.68   7.354%   $163.9081   $163.91   $163.90   $163.90  
  Purchase #5 $140.74   11.159%   $156.4452   $156.45   $156.45   $156.40  
  Purchase #6 $92.92   7.158%   $99.5712   $99.57   $99.55   $99.60  
  Purchase #7 $55.86   6.785%   $59.6501   $59.65   $59.65   $59.70  
  7 purchase totals = $847.03       $920.2873   $920.29   $920.30   $920.30