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 $177.95   7.701%   $191.6539   $191.65   $191.65   $191.70  
  Purchase #2 $136.43   9.656%   $149.6037   $149.60   $149.60   $149.60  
  Purchase #3 $111.49   12.737%   $125.6905   $125.69   $125.70   $125.70  
  Purchase #4 $53.61   10.107%   $59.0284   $59.03   $59.05   $59.00  
  Purchase #5 $115.37   11.153%   $128.2372   $128.24   $128.25   $128.20  
  Purchase #6 $96.62   8.574%   $104.9042   $104.90   $104.90   $104.90  
  Purchase #7 $9.42   8.561%   $10.2264   $10.23   $10.25   $10.20  
  7 purchase totals = $700.89       $769.3443   $769.34   $769.40   $769.30