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 $59.94   13.271%   $67.8946   $67.89   $67.90   $67.90  
  Purchase #2 $50.42   9.137%   $55.0269   $55.03   $55.05   $55.00  
  Purchase #3 $87.49   8.540%   $94.9616   $94.96   $94.95   $95.00  
  Purchase #4 $78.40   7.797%   $84.5128   $84.51   $84.50   $84.50  
  Purchase #5 $249.34   7.125%   $267.1055   $267.11   $267.10   $267.10  
  Purchase #6 $87.41   10.618%   $96.6912   $96.69   $96.70   $96.70  
  Purchase #7 $79.31   6.188%   $84.2177   $84.22   $84.20   $84.20  
  7 purchase totals = $692.31       $750.4103   $750.41   $750.40   $750.40