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 $239.40   9.750%   $262.7415   $262.74   $262.75   $262.70  
  Purchase #2 $62.71   10.333%   $69.1898   $69.19   $69.20   $69.20  
  Purchase #3 $26.37   10.543%   $29.1502   $29.15   $29.15   $29.20  
  Purchase #4 $162.92   13.441%   $184.8181   $184.82   $184.80   $184.80  
  Purchase #5 $98.43   9.173%   $107.459   $107.46   $107.45   $107.50  
  Purchase #6 $67.58   11.341%   $75.2442   $75.24   $75.25   $75.20  
  Purchase #7 $243.92   10.292%   $269.0242   $269.02   $269.00   $269.00  
  7 purchase totals = $901.33       $997.6270   $997.62   $997.60   $997.60