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 $244.58   8.192%   $264.616   $264.62   $264.60   $264.60  
  Purchase #2 $10.34   11.186%   $11.4966   $11.50   $11.50   $11.50  
  Purchase #3 $217.55   12.616%   $244.9961   $245.00   $245.00   $245.00  
  Purchase #4 $45.67   9.863%   $50.1744   $50.17   $50.15   $50.20  
  Purchase #5 $239.80   7.505%   $257.797   $257.80   $257.80   $257.80  
  Purchase #6 $175.70   9.519%   $192.4249   $192.42   $192.40   $192.40  
  Purchase #7 $45.86   3.209%   $47.3316   $47.33   $47.35   $47.30  
  7 purchase totals = $979.50       $1,068.8366   $1,068.84   $1,068.80   $1,068.80