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 $47.73   6.468%   $50.8172   $50.82   $50.80   $50.80  
  Purchase #2 $161.69   8.540%   $175.4983   $175.50   $175.50   $175.50  
  Purchase #3 $58.26   3.865%   $60.5117   $60.51   $60.50   $60.50  
  Purchase #4 $250.26   11.282%   $278.4943   $278.49   $278.50   $278.50  
  Purchase #5 $213.48   5.714%   $225.6782   $225.68   $225.70   $225.70  
  Purchase #6 $204.59   4.553%   $213.905   $213.91   $213.90   $213.90  
  Purchase #7 $184.95   13.104%   $209.1858   $209.19   $209.20   $209.20  
  7 purchase totals = $1,120.96       $1,214.0905   $1,214.10   $1,214.10   $1,214.10