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 $56.39   5.353%   $59.4086   $59.41   $59.40   $59.40  
  Purchase #2 $29.79   6.299%   $31.6665   $31.67   $31.65   $31.70  
  Purchase #3 $116.70   3.474%   $120.7542   $120.75   $120.75   $120.80  
  Purchase #4 $203.39   11.698%   $227.1826   $227.18   $227.20   $227.20  
  Purchase #5 $48.77   7.634%   $52.4931   $52.49   $52.50   $52.50  
  Purchase #6 $103.65   4.167%   $107.9691   $107.97   $107.95   $108.00  
  Purchase #7 $248.92   7.102%   $266.5983   $266.60   $266.60   $266.60  
  7 purchase totals = $807.61       $866.0724   $866.07   $866.05   $866.20