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 $244.65   11.683%   $273.2325   $273.23   $273.25   $273.20  
  Purchase #2 $25.74   7.554%   $27.6844   $27.68   $27.70   $27.70  
  Purchase #3 $90.55   7.784%   $97.5984   $97.60   $97.60   $97.60  
  Purchase #4 $193.94   6.474%   $206.4957   $206.50   $206.50   $206.50  
  Purchase #5 $216.62   12.661%   $244.0463   $244.05   $244.05   $244.00  
  Purchase #6 $13.67   4.712%   $14.3141   $14.31   $14.30   $14.30  
  Purchase #7 $64.99   9.112%   $70.9119   $70.91   $70.90   $70.90  
  7 purchase totals = $850.16       $934.2833   $934.28   $934.30   $934.20