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 $228.28   10.283%   $251.754   $251.75   $251.75   $251.80  
  Purchase #2 $83.35   11.207%   $92.691   $92.69   $92.70   $92.70  
  Purchase #3 $116.57   5.120%   $122.5384   $122.54   $122.55   $122.50  
  Purchase #4 $95.47   4.359%   $99.6315   $99.63   $99.65   $99.60  
  Purchase #5 $13.54   4.761%   $14.1846   $14.18   $14.20   $14.20  
  Purchase #6 $100.27   4.630%   $104.9125   $104.91   $104.90   $104.90  
  Purchase #7 $176.83   4.608%   $184.9783   $184.98   $185.00   $185.00  
  7 purchase totals = $814.31       $870.6903   $870.68   $870.75   $870.70