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 $54.43   4.222%   $56.728   $56.73   $56.75   $56.70  
  Purchase #2 $185.60   10.172%   $204.4792   $204.48   $204.50   $204.50  
  Purchase #3 $53.87   12.766%   $60.747   $60.75   $60.75   $60.70  
  Purchase #4 $29.41   9.181%   $32.1101   $32.11   $32.10   $32.10  
  Purchase #5 $188.61   9.225%   $206.0093   $206.01   $206.00   $206.00  
  Purchase #6 $186.28   3.123%   $192.0975   $192.10   $192.10   $192.10  
  Purchase #7 $179.93   6.872%   $192.2948   $192.29   $192.30   $192.30  
  7 purchase totals = $878.13       $944.4659   $944.47   $944.50   $944.40