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 $32.63   8.418%   $35.3768   $35.38   $35.40   $35.40  
  Purchase #2 $229.86   9.764%   $252.3035   $252.30   $252.30   $252.30  
  Purchase #3 $249.27   13.357%   $282.565   $282.57   $282.55   $282.60  
  Purchase #4 $150.49   13.404%   $170.6617   $170.66   $170.65   $170.70  
  Purchase #5 $250.37   5.287%   $263.6071   $263.61   $263.60   $263.60  
  Purchase #6 $66.96   11.858%   $74.9001   $74.90   $74.90   $74.90  
  Purchase #7 $15.76   11.193%   $17.524   $17.52   $17.50   $17.50  
  7 purchase totals = $995.34       $1,096.9382   $1,096.94   $1,096.90   $1,097.00