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 $225.47   12.627%   $253.9401   $253.94   $253.95   $253.90  
  Purchase #2 $248.69   10.218%   $274.1011   $274.10   $274.10   $274.10  
  Purchase #3 $19.39   11.693%   $21.6573   $21.66   $21.65   $21.70  
  Purchase #4 $47.28   3.303%   $48.8417   $48.84   $48.85   $48.80  
  Purchase #5 $69.52   10.823%   $77.0441   $77.04   $77.05   $77.00  
  Purchase #6 $198.68   13.792%   $226.0819   $226.08   $226.10   $226.10  
  Purchase #7 $48.35   11.410%   $53.8667   $53.87   $53.85   $53.90  
  7 purchase totals = $857.38       $955.5329   $955.53   $955.55   $955.50