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 $239.27   10.873%   $265.2858   $265.29   $265.30   $265.30  
  Purchase #2 $174.85   9.139%   $190.8295   $190.83   $190.85   $190.80  
  Purchase #3 $103.25   12.658%   $116.3194   $116.32   $116.30   $116.30  
  Purchase #4 $249.32   5.193%   $262.2672   $262.27   $262.25   $262.30  
  Purchase #5 $179.59   10.615%   $198.6535   $198.65   $198.65   $198.70  
  Purchase #6 $209.39   7.813%   $225.7496   $225.75   $225.75   $225.70  
  Purchase #7 $17.82   6.843%   $19.0394   $19.04   $19.05   $19.00  
  7 purchase totals = $1,173.49       $1,278.1444   $1,278.15   $1,278.15   $1,278.10