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 $220.98   13.859%   $251.6056   $251.61   $251.60   $251.60  
  Purchase #2 $105.98   5.710%   $112.0315   $112.03   $112.05   $112.00  
  Purchase #3 $91.29   7.209%   $97.8711   $97.87   $97.85   $97.90  
  Purchase #4 $241.55   11.643%   $269.6737   $269.67   $269.65   $269.70  
  Purchase #5 $126.92   4.779%   $132.9855   $132.99   $133.00   $133.00  
  Purchase #6 $77.55   4.750%   $81.2336   $81.23   $81.25   $81.20  
  Purchase #7 $107.85   10.728%   $119.4201   $119.42   $119.40   $119.40  
  7 purchase totals = $972.12       $1,064.8211   $1,064.82   $1,064.80   $1,064.80