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 $202.58   9.209%   $221.2356   $221.24   $221.25   $221.20  
  Purchase #2 $157.86   13.265%   $178.8001   $178.80   $178.80   $178.80  
  Purchase #3 $5.93   9.102%   $6.4697   $6.47   $6.45   $6.50  
  Purchase #4 $113.71   5.825%   $120.3336   $120.33   $120.35   $120.30  
  Purchase #5 $149.47   5.556%   $157.7746   $157.77   $157.75   $157.80  
  Purchase #6 $155.88   6.136%   $165.4448   $165.44   $165.45   $165.40  
  Purchase #7 $177.71   7.762%   $191.5039   $191.50   $191.50   $191.50  
  7 purchase totals = $963.14       $1,041.5623   $1,041.55   $1,041.55   $1,041.50