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 $21.55   7.319%   $23.1272   $23.13   $23.15   $23.10  
  Purchase #2 $237.47   11.505%   $264.7909   $264.79   $264.80   $264.80  
  Purchase #3 $61.29   11.459%   $68.3132   $68.31   $68.30   $68.30  
  Purchase #4 $244.93   8.235%   $265.1   $265.10   $265.10   $265.10  
  Purchase #5 $245.93   5.491%   $259.434   $259.43   $259.45   $259.40  
  Purchase #6 $248.77   8.574%   $270.0995   $270.10   $270.10   $270.10  
  Purchase #7 $101.83   6.405%   $108.3522   $108.35   $108.35   $108.40  
  7 purchase totals = $1,161.77       $1,259.2170   $1,259.21   $1,259.25   $1,259.20