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 $60.70   4.712%   $63.5602   $63.56   $63.55   $63.60  
  Purchase #2 $249.82   6.440%   $265.9084   $265.91   $265.90   $265.90  
  Purchase #3 $52.26   4.832%   $54.7852   $54.79   $54.80   $54.80  
  Purchase #4 $169.55   13.408%   $192.2833   $192.28   $192.30   $192.30  
  Purchase #5 $201.59   6.755%   $215.2074   $215.21   $215.20   $215.20  
  Purchase #6 $233.78   3.414%   $241.7612   $241.76   $241.75   $241.80  
  Purchase #7 $228.95   9.771%   $251.3207   $251.32   $251.30   $251.30  
  7 purchase totals = $1,196.65       $1,284.8264   $1,284.83   $1,284.80   $1,284.90