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 $129.64   7.453%   $139.3021   $139.30   $139.30   $139.30  
  Purchase #2 $127.41   11.132%   $141.5933   $141.59   $141.60   $141.60  
  Purchase #3 $51.95   9.233%   $56.7465   $56.75   $56.75   $56.70  
  Purchase #4 $141.84   12.516%   $159.5927   $159.59   $159.60   $159.60  
  Purchase #5 $225.40   9.807%   $247.505   $247.51   $247.50   $247.50  
  Purchase #6 $78.28   10.602%   $86.5792   $86.58   $86.60   $86.60  
  Purchase #7 $39.51   13.188%   $44.7206   $44.72   $44.70   $44.70  
  7 purchase totals = $794.03       $876.0394   $876.04   $876.05   $876.00