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 $100.52   6.265%   $106.8176   $106.82   $106.80   $106.80  
  Purchase #2 $207.53   10.354%   $229.0177   $229.02   $229.00   $229.00  
  Purchase #3 $149.49   4.852%   $156.7433   $156.74   $156.75   $156.70  
  Purchase #4 $47.39   6.849%   $50.6357   $50.64   $50.65   $50.60  
  Purchase #5 $68.29   7.184%   $73.196   $73.20   $73.20   $73.20  
  Purchase #6 $250.55   7.516%   $269.3813   $269.38   $269.40   $269.40  
  Purchase #7 $57.40   13.763%   $65.3   $65.30   $65.30   $65.30  
  7 purchase totals = $881.17       $951.0916   $951.10   $951.10   $951.00