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 $46.87   5.154%   $49.2857   $49.29   $49.30   $49.30  
  Purchase #2 $218.90   10.113%   $241.0374   $241.04   $241.05   $241.00  
  Purchase #3 $247.64   11.769%   $276.7848   $276.78   $276.80   $276.80  
  Purchase #4 $151.69   13.796%   $172.6172   $172.62   $172.60   $172.60  
  Purchase #5 $60.56   7.249%   $64.95   $64.95   $64.95   $65.00  
  Purchase #6 $179.69   5.698%   $189.9287   $189.93   $189.95   $189.90  
  Purchase #7 $73.89   7.397%   $79.3556   $79.36   $79.35   $79.40  
  7 purchase totals = $979.24       $1,073.9594   $1,073.97   $1,074.00   $1,074.00