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 $235.26   13.592%   $267.2365   $267.24   $267.25   $267.20  
  Purchase #2 $157.45   3.297%   $162.6411   $162.64   $162.65   $162.60  
  Purchase #3 $211.51   6.335%   $224.9092   $224.91   $224.90   $224.90  
  Purchase #4 $119.39   5.574%   $126.0448   $126.04   $126.05   $126.00  
  Purchase #5 $194.80   9.234%   $212.7878   $212.79   $212.80   $212.80  
  Purchase #6 $154.34   12.224%   $173.2065   $173.21   $173.20   $173.20  
  Purchase #7 $216.79   5.294%   $228.2669   $228.27   $228.25   $228.30  
  7 purchase totals = $1,289.54       $1,395.0928   $1,395.10   $1,395.10   $1,395.00