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 $201.44   7.779%   $217.11   $217.11   $217.10   $217.10  
  Purchase #2 $58.93   12.596%   $66.3528   $66.35   $66.35   $66.40  
  Purchase #3 $69.38   5.652%   $73.3014   $73.30   $73.30   $73.30  
  Purchase #4 $143.56   11.309%   $159.7952   $159.80   $159.80   $159.80  
  Purchase #5 $107.46   9.527%   $117.6977   $117.70   $117.70   $117.70  
  Purchase #6 $89.64   9.702%   $98.3369   $98.34   $98.35   $98.30  
  Purchase #7 $179.68   6.295%   $190.9909   $190.99   $191.00   $191.00  
  7 purchase totals = $850.09       $923.5849   $923.59   $923.60   $923.60