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 $117.37   8.170%   $126.9591   $126.96   $126.95   $127.00  
  Purchase #2 $233.34   8.824%   $253.9299   $253.93   $253.95   $253.90  
  Purchase #3 $166.57   12.523%   $187.4296   $187.43   $187.45   $187.40  
  Purchase #4 $56.68   6.547%   $60.3908   $60.39   $60.40   $60.40  
  Purchase #5 $103.55   8.435%   $112.2844   $112.28   $112.30   $112.30  
  Purchase #6 $12.87   4.386%   $13.4345   $13.43   $13.45   $13.40  
  Purchase #7 $238.86   3.431%   $247.0553   $247.06   $247.05   $247.10  
  7 purchase totals = $929.24       $1,001.4836   $1,001.48   $1,001.55   $1,001.50