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 $176.90   13.638%   $201.0256   $201.03   $201.05   $201.00  
  Purchase #2 $238.79   3.846%   $247.9739   $247.97   $247.95   $248.00  
  Purchase #3 $131.68   4.306%   $137.3501   $137.35   $137.35   $137.40  
  Purchase #4 $92.46   6.358%   $98.3386   $98.34   $98.35   $98.30  
  Purchase #5 $54.82   11.279%   $61.0031   $61.00   $61.00   $61.00  
  Purchase #6 $109.40   9.410%   $119.6945   $119.69   $119.70   $119.70  
  Purchase #7 $63.48   3.396%   $65.6358   $65.64   $65.65   $65.60  
  7 purchase totals = $867.53       $931.0216   $931.02   $931.05   $931.00