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 $244.59   9.322%   $267.3907   $267.39   $267.40   $267.40  
  Purchase #2 $33.53   9.279%   $36.6412   $36.64   $36.65   $36.60  
  Purchase #3 $225.32   12.250%   $252.9217   $252.92   $252.90   $252.90  
  Purchase #4 $154.86   7.285%   $166.1416   $166.14   $166.15   $166.10  
  Purchase #5 $88.53   3.546%   $91.6693   $91.67   $91.65   $91.70  
  Purchase #6 $231.94   11.615%   $258.8798   $258.88   $258.90   $258.90  
  Purchase #7 $169.30   10.420%   $186.9411   $186.94   $186.95   $186.90  
  7 purchase totals = $1,148.07       $1,260.5854   $1,260.58   $1,260.60   $1,260.50