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 $244.59   8.815%   $266.1506   $266.15   $266.15   $266.20  
  Purchase #2 $41.53   10.404%   $45.8508   $45.85   $45.85   $45.90  
  Purchase #3 $120.66   8.288%   $130.6603   $130.66   $130.65   $130.70  
  Purchase #4 $15.28   6.505%   $16.274   $16.27   $16.25   $16.30  
  Purchase #5 $234.48   7.358%   $251.733   $251.73   $251.75   $251.70  
  Purchase #6 $104.54   5.705%   $110.504   $110.50   $110.50   $110.50  
  Purchase #7 $240.83   7.124%   $257.9867   $257.99   $258.00   $258.00  
  7 purchase totals = $1,001.91       $1,079.1594   $1,079.15   $1,079.15   $1,079.30