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 $246.86   11.662%   $275.6488   $275.65   $275.65   $275.60  
  Purchase #2 $145.96   10.617%   $161.4566   $161.46   $161.45   $161.50  
  Purchase #3 $132.65   13.383%   $150.4025   $150.40   $150.40   $150.40  
  Purchase #4 $162.60   11.483%   $181.2714   $181.27   $181.25   $181.30  
  Purchase #5 $233.74   8.151%   $252.7921   $252.79   $252.80   $252.80  
  Purchase #6 $55.63   13.140%   $62.9398   $62.94   $62.95   $62.90  
  Purchase #7 $143.68   5.609%   $151.739   $151.74   $151.75   $151.70  
  7 purchase totals = $1,121.12       $1,236.2502   $1,236.25   $1,236.25   $1,236.20