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 $226.68   6.298%   $240.9563   $240.96   $240.95   $241.00  
  Purchase #2 $92.30   9.296%   $100.8802   $100.88   $100.90   $100.90  
  Purchase #3 $188.96   11.787%   $211.2327   $211.23   $211.25   $211.20  
  Purchase #4 $239.69   11.687%   $267.7026   $267.70   $267.70   $267.70  
  Purchase #5 $141.35   4.317%   $147.4521   $147.45   $147.45   $147.50  
  Purchase #6 $197.42   8.282%   $213.7703   $213.77   $213.75   $213.80  
  Purchase #7 $111.71   6.669%   $119.1599   $119.16   $119.15   $119.20  
  7 purchase totals = $1,198.11       $1,301.1541   $1,301.15   $1,301.15   $1,301.30