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 $244.99   8.544%   $265.9219   $265.92   $265.90   $265.90  
  Purchase #2 $119.94   3.757%   $124.4461   $124.45   $124.45   $124.40  
  Purchase #3 $108.57   11.792%   $121.3726   $121.37   $121.35   $121.40  
  Purchase #4 $223.83   5.403%   $235.9235   $235.92   $235.90   $235.90  
  Purchase #5 $110.57   6.429%   $117.6785   $117.68   $117.70   $117.70  
  Purchase #6 $163.25   3.735%   $169.3474   $169.35   $169.35   $169.30  
  Purchase #7 $156.45   9.834%   $171.8353   $171.84   $171.85   $171.80  
  7 purchase totals = $1,127.60       $1,206.5253   $1,206.53   $1,206.50   $1,206.40