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 $227.29   6.807%   $242.7616   $242.76   $242.75   $242.80  
  Purchase #2 $41.47   4.700%   $43.4191   $43.42   $43.40   $43.40  
  Purchase #3 $238.87   12.217%   $268.0527   $268.05   $268.05   $268.10  
  Purchase #4 $211.37   4.445%   $220.7654   $220.77   $220.75   $220.80  
  Purchase #5 $82.91   11.627%   $92.5499   $92.55   $92.55   $92.50  
  Purchase #6 $192.98   11.259%   $214.7076   $214.71   $214.70   $214.70  
  Purchase #7 $58.96   5.225%   $62.0407   $62.04   $62.05   $62.00  
  7 purchase totals = $1,053.85       $1,144.2970   $1,144.30   $1,144.25   $1,144.30