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 $244.64   9.796%   $268.6049   $268.60   $268.60   $268.60  
  Purchase #2 $32.81   3.183%   $33.8543   $33.85   $33.85   $33.90  
  Purchase #3 $185.88   11.193%   $206.6855   $206.69   $206.70   $206.70  
  Purchase #4 $106.26   6.869%   $113.559   $113.56   $113.55   $113.60  
  Purchase #5 $71.59   8.162%   $77.4332   $77.43   $77.45   $77.40  
  Purchase #6 $29.62   7.779%   $31.9241   $31.92   $31.90   $31.90  
  Purchase #7 $226.98   6.682%   $242.1468   $242.15   $242.15   $242.10  
  7 purchase totals = $897.78       $974.2078   $974.20   $974.20   $974.20