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 $207.60   8.354%   $224.9429   $224.94   $224.95   $224.90  
  Purchase #2 $45.41   12.470%   $51.0726   $51.07   $51.05   $51.10  
  Purchase #3 $119.86   13.193%   $135.6731   $135.67   $135.65   $135.70  
  Purchase #4 $58.98   9.498%   $64.5819   $64.58   $64.60   $64.60  
  Purchase #5 $203.86   11.285%   $226.8656   $226.87   $226.85   $226.90  
  Purchase #6 $212.85   7.780%   $229.4097   $229.41   $229.40   $229.40  
  Purchase #7 $30.84   4.696%   $32.2882   $32.29   $32.30   $32.30  
  7 purchase totals = $879.40       $964.8340   $964.83   $964.80   $964.90