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 $44.44   4.638%   $46.5011   $46.50   $46.50   $46.50  
  Purchase #2 $82.44   6.290%   $87.6255   $87.63   $87.65   $87.60  
  Purchase #3 $111.67   9.564%   $122.3501   $122.35   $122.35   $122.40  
  Purchase #4 $90.34   6.570%   $96.2753   $96.28   $96.30   $96.30  
  Purchase #5 $162.80   6.791%   $173.8557   $173.86   $173.85   $173.90  
  Purchase #6 $137.53   6.812%   $146.8985   $146.90   $146.90   $146.90  
  Purchase #7 $229.44   6.164%   $243.5827   $243.58   $243.60   $243.60  
  7 purchase totals = $858.66       $917.0889   $917.10   $917.15   $917.20