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 $107.55   8.229%   $116.4003   $116.40   $116.40   $116.40  
  Purchase #2 $223.36   10.118%   $245.9596   $245.96   $245.95   $246.00  
  Purchase #3 $64.92   4.657%   $67.9433   $67.94   $67.95   $67.90  
  Purchase #4 $169.36   7.226%   $181.598   $181.60   $181.60   $181.60  
  Purchase #5 $129.45   7.523%   $139.1885   $139.19   $139.20   $139.20  
  Purchase #6 $114.32   6.103%   $121.2969   $121.30   $121.30   $121.30  
  Purchase #7 $137.79   3.160%   $142.1442   $142.14   $142.15   $142.10  
  7 purchase totals = $946.75       $1,014.5308   $1,014.53   $1,014.55   $1,014.50