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 $46.85   6.856%   $50.062   $50.06   $50.05   $50.10  
  Purchase #2 $230.76   7.381%   $247.7924   $247.79   $247.80   $247.80  
  Purchase #3 $68.58   12.350%   $77.0496   $77.05   $77.05   $77.00  
  Purchase #4 $23.30   6.179%   $24.7397   $24.74   $24.75   $24.70  
  Purchase #5 $66.72   9.584%   $73.1144   $73.11   $73.10   $73.10  
  Purchase #6 $41.48   11.860%   $46.3995   $46.40   $46.40   $46.40  
  Purchase #7 $153.47   3.696%   $159.1423   $159.14   $159.15   $159.10  
  7 purchase totals = $631.16       $678.2999   $678.29   $678.30   $678.20