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 $84.58   12.127%   $94.837   $94.84   $94.85   $94.80  
  Purchase #2 $156.87   12.214%   $176.0301   $176.03   $176.05   $176.00  
  Purchase #3 $87.70   8.203%   $94.894   $94.89   $94.90   $94.90  
  Purchase #4 $70.77   9.223%   $77.2971   $77.30   $77.30   $77.30  
  Purchase #5 $174.67   10.703%   $193.3649   $193.36   $193.35   $193.40  
  Purchase #6 $228.47   3.242%   $235.877   $235.88   $235.90   $235.90  
  Purchase #7 $55.32   12.392%   $62.1753   $62.18   $62.20   $62.20  
  7 purchase totals = $858.38       $934.4754   $934.48   $934.55   $934.50