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 $246.27   7.859%   $265.6244   $265.62   $265.60   $265.60  
  Purchase #2 $195.89   3.356%   $202.4641   $202.46   $202.45   $202.50  
  Purchase #3 $114.49   7.426%   $122.992   $122.99   $123.00   $123.00  
  Purchase #4 $134.91   3.128%   $139.13   $139.13   $139.15   $139.10  
  Purchase #5 $14.37   13.828%   $16.3571   $16.36   $16.35   $16.40  
  Purchase #6 $85.34   6.803%   $91.1457   $91.15   $91.15   $91.10  
  Purchase #7 $154.90   9.227%   $169.1926   $169.19   $169.20   $169.20  
  7 purchase totals = $946.17       $1,006.9059   $1,006.90   $1,006.90   $1,006.90