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 $88.89   8.775%   $96.6901   $96.69   $96.70   $96.70  
  Purchase #2 $124.79   10.269%   $137.6047   $137.60   $137.60   $137.60  
  Purchase #3 $175.34   6.751%   $187.1772   $187.18   $187.20   $187.20  
  Purchase #4 $82.26   12.248%   $92.3352   $92.34   $92.35   $92.30  
  Purchase #5 $158.75   10.415%   $175.2838   $175.28   $175.30   $175.30  
  Purchase #6 $200.78   3.638%   $208.0844   $208.08   $208.10   $208.10  
  Purchase #7 $91.68   7.604%   $98.6513   $98.65   $98.65   $98.70  
  7 purchase totals = $922.49       $995.8267   $995.82   $995.90   $995.90