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 $93.32   5.534%   $98.4843   $98.48   $98.50   $98.50  
  Purchase #2 $239.33   7.108%   $256.3416   $256.34   $256.35   $256.30  
  Purchase #3 $32.88   3.231%   $33.9424   $33.94   $33.95   $33.90  
  Purchase #4 $61.95   4.330%   $64.6324   $64.63   $64.65   $64.60  
  Purchase #5 $36.44   7.541%   $39.1879   $39.19   $39.20   $39.20  
  Purchase #6 $220.92   11.497%   $246.3192   $246.32   $246.30   $246.30  
  Purchase #7 $241.51   10.809%   $267.6148   $267.61   $267.60   $267.60  
  7 purchase totals = $926.35       $1,006.5226   $1,006.51   $1,006.55   $1,006.40