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 $227.41   10.694%   $251.7292   $251.73   $251.75   $251.70  
  Purchase #2 $147.82   8.203%   $159.9457   $159.95   $159.95   $159.90  
  Purchase #3 $36.90   10.610%   $40.8151   $40.82   $40.80   $40.80  
  Purchase #4 $246.45   5.436%   $259.847   $259.85   $259.85   $259.80  
  Purchase #5 $57.35   6.218%   $60.916   $60.92   $60.90   $60.90  
  Purchase #6 $167.99   5.299%   $176.8918   $176.89   $176.90   $176.90  
  Purchase #7 $160.50   7.330%   $172.2647   $172.26   $172.25   $172.30  
  7 purchase totals = $1,044.42       $1,122.4095   $1,122.42   $1,122.40   $1,122.30