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 $104.40   13.743%   $118.7477   $118.75   $118.75   $118.70  
  Purchase #2 $148.33   12.299%   $166.5731   $166.57   $166.55   $166.60  
  Purchase #3 $145.80   7.369%   $156.544   $156.54   $156.55   $156.50  
  Purchase #4 $149.64   13.786%   $170.2694   $170.27   $170.25   $170.30  
  Purchase #5 $226.42   7.195%   $242.7109   $242.71   $242.70   $242.70  
  Purchase #6 $64.58   11.808%   $72.2056   $72.21   $72.20   $72.20  
  Purchase #7 $222.68   11.334%   $247.9186   $247.92   $247.90   $247.90  
  7 purchase totals = $1,061.85       $1,174.9693   $1,174.97   $1,174.90   $1,174.90