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 $83.90   11.632%   $93.6592   $93.66   $93.65   $93.70  
  Purchase #2 $85.63   7.442%   $92.0026   $92.00   $92.00   $92.00  
  Purchase #3 $59.68   9.508%   $65.3544   $65.35   $65.35   $65.40  
  Purchase #4 $240.65   11.460%   $268.2285   $268.23   $268.25   $268.20  
  Purchase #5 $89.99   6.530%   $95.8663   $95.87   $95.85   $95.90  
  Purchase #6 $120.59   3.196%   $124.4441   $124.44   $124.45   $124.40  
  Purchase #7 $71.58   6.798%   $76.446   $76.45   $76.45   $76.40  
  7 purchase totals = $752.02       $816.0011   $816.00   $816.00   $816.00