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 $249.28   5.394%   $262.7262   $262.73   $262.75   $262.70  
  Purchase #2 $107.99   7.799%   $116.4121   $116.41   $116.40   $116.40  
  Purchase #3 $30.54   9.810%   $33.536   $33.54   $33.55   $33.50  
  Purchase #4 $147.74   8.114%   $159.7276   $159.73   $159.75   $159.70  
  Purchase #5 $49.67   12.842%   $56.0486   $56.05   $56.05   $56.00  
  Purchase #6 $248.34   11.421%   $276.7029   $276.70   $276.70   $276.70  
  Purchase #7 $44.43   10.656%   $49.1645   $49.16   $49.15   $49.20  
  7 purchase totals = $877.99       $954.3179   $954.32   $954.35   $954.20