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 $86.85   6.535%   $92.5256   $92.53   $92.55   $92.50  
  Purchase #2 $239.28   11.550%   $266.9168   $266.92   $266.90   $266.90  
  Purchase #3 $48.44   13.241%   $54.8539   $54.85   $54.85   $54.90  
  Purchase #4 $35.92   8.212%   $38.8698   $38.87   $38.85   $38.90  
  Purchase #5 $106.82   6.522%   $113.7868   $113.79   $113.80   $113.80  
  Purchase #6 $182.65   5.457%   $192.6172   $192.62   $192.60   $192.60  
  Purchase #7 $181.73   8.508%   $197.1916   $197.19   $197.20   $197.20  
  7 purchase totals = $881.69       $956.7617   $956.77   $956.75   $956.80