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 $237.49   11.865%   $265.6682   $265.67   $265.65   $265.70  
  Purchase #2 $46.85   8.741%   $50.9452   $50.95   $50.95   $50.90  
  Purchase #3 $89.96   8.824%   $97.8981   $97.90   $97.90   $97.90  
  Purchase #4 $232.86   7.502%   $250.3292   $250.33   $250.35   $250.30  
  Purchase #5 $96.49   9.122%   $105.2918   $105.29   $105.30   $105.30  
  Purchase #6 $14.27   12.107%   $15.9977   $16.00   $16.00   $16.00  
  Purchase #7 $131.55   5.418%   $138.6774   $138.68   $138.70   $138.70  
  7 purchase totals = $849.47       $924.8076   $924.82   $924.85   $924.80