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 $68.96   12.470%   $77.5593   $77.56   $77.55   $77.60  
  Purchase #2 $230.90   6.410%   $245.7007   $245.70   $245.70   $245.70  
  Purchase #3 $53.62   3.200%   $55.3358   $55.34   $55.35   $55.30  
  Purchase #4 $104.76   11.241%   $116.5361   $116.54   $116.55   $116.50  
  Purchase #5 $204.53   8.698%   $222.32   $222.32   $222.30   $222.30  
  Purchase #6 $193.80   8.841%   $210.9339   $210.93   $210.95   $210.90  
  Purchase #7 $20.27   5.596%   $21.4043   $21.40   $21.40   $21.40  
  7 purchase totals = $876.84       $949.7901   $949.79   $949.80   $949.70