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 $221.34   11.220%   $246.1743   $246.17   $246.15   $246.20  
  Purchase #2 $86.51   9.595%   $94.8106   $94.81   $94.80   $94.80  
  Purchase #3 $104.53   3.124%   $107.7955   $107.80   $107.80   $107.80  
  Purchase #4 $48.89   11.270%   $54.3999   $54.40   $54.40   $54.40  
  Purchase #5 $245.53   7.382%   $263.655   $263.66   $263.65   $263.70  
  Purchase #6 $206.50   3.412%   $213.5458   $213.55   $213.55   $213.50  
  Purchase #7 $6.97   8.749%   $7.5798   $7.58   $7.60   $7.60  
  7 purchase totals = $920.27       $987.9609   $987.97   $987.95   $988.00