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 $61.91   6.493%   $65.9298   $65.93   $65.95   $65.90  
  Purchase #2 $232.89   13.859%   $265.1662   $265.17   $265.15   $265.20  
  Purchase #3 $5.65   11.157%   $6.2804   $6.28   $6.30   $6.30  
  Purchase #4 $64.26   13.292%   $72.8014   $72.80   $72.80   $72.80  
  Purchase #5 $160.39   13.712%   $182.3827   $182.38   $182.40   $182.40  
  Purchase #6 $241.82   13.461%   $274.3714   $274.37   $274.35   $274.40  
  Purchase #7 $37.63   4.168%   $39.1984   $39.20   $39.20   $39.20  
  7 purchase totals = $804.55       $906.1303   $906.13   $906.15   $906.20