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 $82.98   13.691%   $94.3408   $94.34   $94.35   $94.30  
  Purchase #2 $193.86   11.342%   $215.8476   $215.85   $215.85   $215.80  
  Purchase #3 $234.96   8.805%   $255.6482   $255.65   $255.65   $255.60  
  Purchase #4 $57.50   7.564%   $61.8493   $61.85   $61.85   $61.80  
  Purchase #5 $185.58   3.541%   $192.1514   $192.15   $192.15   $192.20  
  Purchase #6 $9.34   10.281%   $10.3002   $10.30   $10.30   $10.30  
  Purchase #7 $207.68   9.752%   $227.933   $227.93   $227.95   $227.90  
  7 purchase totals = $971.90       $1,058.0705   $1,058.07   $1,058.10   $1,057.90