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 $108.70   10.268%   $119.8613   $119.86   $119.85   $119.90  
  Purchase #2 $181.83   4.553%   $190.1087   $190.11   $190.10   $190.10  
  Purchase #3 $239.75   10.859%   $265.7845   $265.78   $265.80   $265.80  
  Purchase #4 $174.87   8.284%   $189.3562   $189.36   $189.35   $189.40  
  Purchase #5 $95.88   13.341%   $108.6714   $108.67   $108.65   $108.70  
  Purchase #6 $208.90   9.604%   $228.9628   $228.96   $228.95   $229.00  
  Purchase #7 $157.95   9.573%   $173.0706   $173.07   $173.05   $173.10  
  7 purchase totals = $1,167.88       $1,275.8155   $1,275.81   $1,275.75   $1,276.00