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 $118.61   6.229%   $125.9982   $126.00   $126.00   $126.00  
  Purchase #2 $141.32   8.299%   $153.0481   $153.05   $153.05   $153.00  
  Purchase #3 $30.91   8.453%   $33.5228   $33.52   $33.50   $33.50  
  Purchase #4 $174.82   13.659%   $198.6987   $198.70   $198.70   $198.70  
  Purchase #5 $193.59   5.857%   $204.9286   $204.93   $204.95   $204.90  
  Purchase #6 $35.93   8.363%   $38.9348   $38.93   $38.95   $38.90  
  Purchase #7 $173.71   4.637%   $181.7649   $181.76   $181.75   $181.80  
  7 purchase totals = $868.89       $936.8961   $936.89   $936.90   $936.80