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 $23.87   3.719%   $24.7577   $24.76   $24.75   $24.80  
  Purchase #2 $56.33   8.181%   $60.9384   $60.94   $60.95   $60.90  
  Purchase #3 $220.99   13.415%   $250.6358   $250.64   $250.65   $250.60  
  Purchase #4 $52.74   13.356%   $59.784   $59.78   $59.80   $59.80  
  Purchase #5 $9.99   3.313%   $10.321   $10.32   $10.30   $10.30  
  Purchase #6 $116.72   7.164%   $125.0818   $125.08   $125.10   $125.10  
  Purchase #7 $15.40   5.817%   $16.2958   $16.30   $16.30   $16.30  
  7 purchase totals = $496.04       $547.8145   $547.82   $547.85   $547.80