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 $105.75   11.198%   $117.5919   $117.59   $117.60   $117.60  
  Purchase #2 $248.74   6.533%   $264.9902   $264.99   $265.00   $265.00  
  Purchase #3 $18.26   11.137%   $20.2936   $20.29   $20.30   $20.30  
  Purchase #4 $196.42   3.675%   $203.6384   $203.64   $203.65   $203.60  
  Purchase #5 $51.65   3.770%   $53.5972   $53.60   $53.60   $53.60  
  Purchase #6 $50.56   8.852%   $55.0356   $55.04   $55.05   $55.00  
  Purchase #7 $10.67   8.400%   $11.5663   $11.57   $11.55   $11.60  
  7 purchase totals = $682.05       $726.7132   $726.72   $726.75   $726.70