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 $86.42   12.169%   $96.9364   $96.94   $96.95   $96.90  
  Purchase #2 $249.40   8.414%   $270.3845   $270.38   $270.40   $270.40  
  Purchase #3 $193.99   12.482%   $218.2038   $218.20   $218.20   $218.20  
  Purchase #4 $114.52   9.807%   $125.751   $125.75   $125.75   $125.80  
  Purchase #5 $216.50   13.581%   $245.9029   $245.90   $245.90   $245.90  
  Purchase #6 $108.45   10.325%   $119.6475   $119.65   $119.65   $119.60  
  Purchase #7 $233.75   5.657%   $246.9732   $246.97   $246.95   $247.00  
  7 purchase totals = $1,203.03       $1,323.7993   $1,323.79   $1,323.80   $1,323.80