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 $188.49   8.462%   $204.44   $204.44   $204.45   $204.40  
  Purchase #2 $231.47   11.337%   $257.7118   $257.71   $257.70   $257.70  
  Purchase #3 $66.38   4.663%   $69.4753   $69.48   $69.50   $69.50  
  Purchase #4 $223.98   3.427%   $231.6558   $231.66   $231.65   $231.70  
  Purchase #5 $192.83   9.183%   $210.5376   $210.54   $210.55   $210.50  
  Purchase #6 $173.83   4.823%   $182.2138   $182.21   $182.20   $182.20  
  Purchase #7 $110.99   6.364%   $118.0534   $118.05   $118.05   $118.10  
  7 purchase totals = $1,187.97       $1,274.0877   $1,274.09   $1,274.10   $1,274.10