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 $88.61   11.132%   $98.4741   $98.47   $98.45   $98.50  
  Purchase #2 $189.71   9.197%   $207.1576   $207.16   $207.15   $207.20  
  Purchase #3 $174.95   11.535%   $195.1305   $195.13   $195.15   $195.10  
  Purchase #4 $113.98   8.284%   $123.4221   $123.42   $123.40   $123.40  
  Purchase #5 $207.88   9.405%   $227.4311   $227.43   $227.45   $227.40  
  Purchase #6 $211.56   3.364%   $218.6769   $218.68   $218.70   $218.70  
  Purchase #7 $198.80   9.120%   $216.9306   $216.93   $216.95   $216.90  
  7 purchase totals = $1,185.49       $1,287.2229   $1,287.22   $1,287.25   $1,287.20