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 $56.45   8.823%   $61.4306   $61.43   $61.45   $61.40  
  Purchase #2 $185.96   4.725%   $194.7466   $194.75   $194.75   $194.70  
  Purchase #3 $34.27   11.860%   $38.3344   $38.33   $38.35   $38.30  
  Purchase #4 $32.68   12.688%   $36.8264   $36.83   $36.85   $36.80  
  Purchase #5 $86.37   12.349%   $97.0358   $97.04   $97.05   $97.00  
  Purchase #6 $246.64   5.180%   $259.416   $259.42   $259.40   $259.40  
  Purchase #7 $210.27   4.168%   $219.0341   $219.03   $219.05   $219.00  
  7 purchase totals = $852.64       $906.8239   $906.83   $906.90   $906.60