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 $34.76   7.361%   $37.3187   $37.32   $37.30   $37.30  
  Purchase #2 $115.43   3.397%   $119.3512   $119.35   $119.35   $119.40  
  Purchase #3 $245.77   12.198%   $275.749   $275.75   $275.75   $275.70  
  Purchase #4 $29.33   6.515%   $31.2408   $31.24   $31.25   $31.20  
  Purchase #5 $174.37   11.651%   $194.6858   $194.69   $194.70   $194.70  
  Purchase #6 $135.71   6.395%   $144.3887   $144.39   $144.40   $144.40  
  Purchase #7 $145.81   11.770%   $162.9718   $162.97   $162.95   $163.00  
  7 purchase totals = $881.18       $965.7060   $965.71   $965.70   $965.70