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 $168.98   13.187%   $191.2634   $191.26   $191.25   $191.30  
  Purchase #2 $119.89   4.795%   $125.6387   $125.64   $125.65   $125.60  
  Purchase #3 $201.60   7.322%   $216.3612   $216.36   $216.35   $216.40  
  Purchase #4 $177.65   11.168%   $197.49   $197.49   $197.50   $197.50  
  Purchase #5 $240.58   12.438%   $270.5033   $270.50   $270.50   $270.50  
  Purchase #6 $94.91   5.864%   $100.4755   $100.48   $100.50   $100.50  
  Purchase #7 $81.39   6.315%   $86.5298   $86.53   $86.55   $86.50  
  7 purchase totals = $1,085.00       $1,188.2619   $1,188.26   $1,188.30   $1,188.30