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 $86.46   8.319%   $93.6526   $93.65   $93.65   $93.70  
  Purchase #2 $129.98   10.502%   $143.6305   $143.63   $143.65   $143.60  
  Purchase #3 $200.57   11.117%   $222.8674   $222.87   $222.85   $222.90  
  Purchase #4 $84.59   9.530%   $92.6514   $92.65   $92.65   $92.70  
  Purchase #5 $123.59   12.319%   $138.8151   $138.82   $138.80   $138.80  
  Purchase #6 $199.32   4.760%   $208.8076   $208.81   $208.80   $208.80  
  Purchase #7 $77.82   7.739%   $83.8425   $83.84   $83.85   $83.80  
  7 purchase totals = $902.33       $984.2671   $984.27   $984.25   $984.30