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 $215.93   8.129%   $233.4829   $233.48   $233.50   $233.50  
  Purchase #2 $144.69   7.161%   $155.0513   $155.05   $155.05   $155.10  
  Purchase #3 $68.33   10.804%   $75.7124   $75.71   $75.70   $75.70  
  Purchase #4 $189.49   10.260%   $208.9317   $208.93   $208.95   $208.90  
  Purchase #5 $115.96   9.333%   $126.7825   $126.78   $126.80   $126.80  
  Purchase #6 $103.89   13.493%   $117.9079   $117.91   $117.90   $117.90  
  Purchase #7 $95.79   11.435%   $106.7436   $106.74   $106.75   $106.70  
  7 purchase totals = $934.08       $1,024.6123   $1,024.60   $1,024.65   $1,024.60