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 $63.67   13.691%   $72.3871   $72.39   $72.40   $72.40  
  Purchase #2 $181.96   9.874%   $199.9267   $199.93   $199.95   $199.90  
  Purchase #3 $194.81   6.259%   $207.0032   $207.00   $207.00   $207.00  
  Purchase #4 $17.51   4.662%   $18.3263   $18.33   $18.35   $18.30  
  Purchase #5 $247.57   13.134%   $280.0858   $280.09   $280.10   $280.10  
  Purchase #6 $112.29   7.285%   $120.4703   $120.47   $120.45   $120.50  
  Purchase #7 $58.66   10.535%   $64.8398   $64.84   $64.85   $64.80  
  7 purchase totals = $876.47       $963.0392   $963.05   $963.10   $963.00