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 $227.69   6.728%   $243.009   $243.01   $243.00   $243.00  
  Purchase #2 $164.98   4.666%   $172.678   $172.68   $172.70   $172.70  
  Purchase #3 $82.36   10.802%   $91.2565   $91.26   $91.25   $91.30  
  Purchase #4 $166.36   9.776%   $182.6234   $182.62   $182.60   $182.60  
  Purchase #5 $133.50   3.394%   $138.031   $138.03   $138.05   $138.00  
  Purchase #6 $122.29   9.318%   $133.685   $133.69   $133.70   $133.70  
  Purchase #7 $40.72   5.866%   $43.1086   $43.11   $43.10   $43.10  
  7 purchase totals = $937.90       $1,004.3915   $1,004.40   $1,004.40   $1,004.40