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 $60.69   10.843%   $67.2706   $67.27   $67.25   $67.30  
  Purchase #2 $206.29   5.461%   $217.5555   $217.56   $217.55   $217.60  
  Purchase #3 $196.31   8.569%   $213.1318   $213.13   $213.15   $213.10  
  Purchase #4 $227.26   3.125%   $234.3619   $234.36   $234.35   $234.40  
  Purchase #5 $197.58   5.231%   $207.9154   $207.92   $207.90   $207.90  
  Purchase #6 $107.97   12.279%   $121.2276   $121.23   $121.25   $121.20  
  Purchase #7 $79.77   4.217%   $83.1339   $83.13   $83.15   $83.10  
  7 purchase totals = $1,075.87       $1,144.5967   $1,144.60   $1,144.60   $1,144.60