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 $220.69   11.243%   $245.5022   $245.50   $245.50   $245.50  
  Purchase #2 $42.75   9.161%   $46.6663   $46.67   $46.65   $46.70  
  Purchase #3 $181.70   4.199%   $189.3296   $189.33   $189.35   $189.30  
  Purchase #4 $87.67   12.210%   $98.3745   $98.37   $98.35   $98.40  
  Purchase #5 $250.84   11.589%   $279.9098   $279.91   $279.90   $279.90  
  Purchase #6 $44.54   6.264%   $47.33   $47.33   $47.35   $47.30  
  Purchase #7 $25.44   4.346%   $26.5456   $26.55   $26.55   $26.50  
  7 purchase totals = $853.63       $933.6580   $933.66   $933.65   $933.60