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 $215.35   8.226%   $233.0647   $233.06   $233.05   $233.10  
  Purchase #2 $32.28   12.413%   $36.2869   $36.29   $36.30   $36.30  
  Purchase #3 $16.49   12.668%   $18.579   $18.58   $18.60   $18.60  
  Purchase #4 $63.47   7.215%   $68.0494   $68.05   $68.05   $68.00  
  Purchase #5 $189.92   11.339%   $211.455   $211.46   $211.45   $211.50  
  Purchase #6 $129.90   13.704%   $147.7015   $147.70   $147.70   $147.70  
  Purchase #7 $43.96   3.396%   $45.4529   $45.45   $45.45   $45.50  
  7 purchase totals = $691.37       $760.5894   $760.59   $760.60   $760.70