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 $68.43   10.781%   $75.8074   $75.81   $75.80   $75.80  
  Purchase #2 $244.27   12.513%   $274.8355   $274.84   $274.85   $274.80  
  Purchase #3 $88.45   5.445%   $93.2661   $93.27   $93.25   $93.30  
  Purchase #4 $45.29   7.252%   $48.5744   $48.57   $48.55   $48.60  
  Purchase #5 $158.85   9.326%   $173.6644   $173.66   $173.65   $173.70  
  Purchase #6 $57.59   9.644%   $63.144   $63.14   $63.15   $63.10  
  Purchase #7 $234.94   9.262%   $256.7001   $256.70   $256.70   $256.70  
  7 purchase totals = $897.82       $985.9919   $985.99   $985.95   $986.00