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 $59.74   7.476%   $64.2062   $64.21   $64.20   $64.20  
  Purchase #2 $217.95   13.232%   $246.7891   $246.79   $246.80   $246.80  
  Purchase #3 $205.54   10.427%   $226.9717   $226.97   $226.95   $227.00  
  Purchase #4 $58.47   10.505%   $64.6123   $64.61   $64.60   $64.60  
  Purchase #5 $74.72   5.769%   $79.0306   $79.03   $79.05   $79.00  
  Purchase #6 $127.81   11.769%   $142.852   $142.85   $142.85   $142.90  
  Purchase #7 $116.28   11.371%   $129.5022   $129.50   $129.50   $129.50  
  7 purchase totals = $860.51       $953.9641   $953.96   $953.95   $954.00