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 $238.43   9.281%   $260.5587   $260.56   $260.55   $260.60  
  Purchase #2 $139.47   6.129%   $148.0181   $148.02   $148.00   $148.00  
  Purchase #3 $155.85   4.172%   $162.3521   $162.35   $162.35   $162.40  
  Purchase #4 $209.86   6.714%   $223.95   $223.95   $223.95   $224.00  
  Purchase #5 $130.60   5.625%   $137.9463   $137.95   $137.95   $137.90  
  Purchase #6 $207.67   9.117%   $226.6033   $226.60   $226.60   $226.60  
  Purchase #7 $129.56   5.107%   $136.1766   $136.18   $136.20   $136.20  
  7 purchase totals = $1,211.44       $1,295.6051   $1,295.61   $1,295.60   $1,295.70