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 $246.91   8.410%   $267.6751   $267.68   $267.70   $267.70  
  Purchase #2 $45.74   8.423%   $49.5927   $49.59   $49.60   $49.60  
  Purchase #3 $181.60   11.403%   $202.3078   $202.31   $202.30   $202.30  
  Purchase #4 $206.93   9.787%   $227.1822   $227.18   $227.20   $227.20  
  Purchase #5 $84.97   6.609%   $90.5857   $90.59   $90.60   $90.60  
  Purchase #6 $140.76   5.659%   $148.7256   $148.73   $148.75   $148.70  
  Purchase #7 $48.82   6.359%   $51.9245   $51.92   $51.90   $51.90  
  7 purchase totals = $955.73       $1,037.9936   $1,038.00   $1,038.05   $1,038.00