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 $193.78   12.121%   $217.2681   $217.27   $217.25   $217.30  
  Purchase #2 $191.93   6.262%   $203.9487   $203.95   $203.95   $203.90  
  Purchase #3 $69.79   3.215%   $72.0337   $72.03   $72.05   $72.00  
  Purchase #4 $16.64   4.356%   $17.3648   $17.36   $17.35   $17.40  
  Purchase #5 $163.95   13.362%   $185.857   $185.86   $185.85   $185.90  
  Purchase #6 $86.28   6.319%   $91.732   $91.73   $91.75   $91.70  
  Purchase #7 $194.47   8.422%   $210.8483   $210.85   $210.85   $210.80  
  7 purchase totals = $916.84       $999.0526   $999.05   $999.05   $999.00