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 $94.65   12.391%   $106.3781   $106.38   $106.40   $106.40  
  Purchase #2 $23.93   9.585%   $26.2237   $26.22   $26.20   $26.20  
  Purchase #3 $131.43   4.151%   $136.8857   $136.89   $136.90   $136.90  
  Purchase #4 $204.47   6.532%   $217.826   $217.83   $217.85   $217.80  
  Purchase #5 $119.37   11.797%   $133.4521   $133.45   $133.45   $133.50  
  Purchase #6 $196.40   12.658%   $221.2603   $221.26   $221.25   $221.30  
  Purchase #7 $199.60   8.391%   $216.3484   $216.35   $216.35   $216.30  
  7 purchase totals = $969.85       $1,058.3743   $1,058.38   $1,058.40   $1,058.40