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 $246.79   7.771%   $265.9681   $265.97   $265.95   $266.00  
  Purchase #2 $246.71   10.213%   $271.9065   $271.91   $271.90   $271.90  
  Purchase #3 $205.79   3.485%   $212.9618   $212.96   $212.95   $213.00  
  Purchase #4 $187.58   12.780%   $211.5527   $211.55   $211.55   $211.60  
  Purchase #5 $136.86   11.565%   $152.6879   $152.69   $152.70   $152.70  
  Purchase #6 $45.70   11.357%   $50.8901   $50.89   $50.90   $50.90  
  Purchase #7 $225.87   6.770%   $241.1614   $241.16   $241.15   $241.20  
  7 purchase totals = $1,295.30       $1,407.1285   $1,407.13   $1,407.10   $1,407.30