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 $67.36   10.151%   $74.1977   $74.20   $74.20   $74.20  
  Purchase #2 $53.94   6.290%   $57.3328   $57.33   $57.35   $57.30  
  Purchase #3 $231.71   5.752%   $245.038   $245.04   $245.05   $245.00  
  Purchase #4 $52.39   8.820%   $57.0108   $57.01   $57.00   $57.00  
  Purchase #5 $192.32   3.207%   $198.4877   $198.49   $198.50   $198.50  
  Purchase #6 $62.82   8.587%   $68.2144   $68.21   $68.20   $68.20  
  Purchase #7 $9.51   7.847%   $10.2562   $10.26   $10.25   $10.30  
  7 purchase totals = $670.05       $710.5376   $710.54   $710.55   $710.50