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 $63.25   6.377%   $67.2835   $67.28   $67.30   $67.30  
  Purchase #2 $134.73   3.374%   $139.2758   $139.28   $139.30   $139.30  
  Purchase #3 $23.42   3.480%   $24.235   $24.24   $24.25   $24.20  
  Purchase #4 $86.55   10.858%   $95.9476   $95.95   $95.95   $95.90  
  Purchase #5 $211.38   11.337%   $235.3442   $235.34   $235.35   $235.30  
  Purchase #6 $180.52   12.801%   $203.6284   $203.63   $203.65   $203.60  
  Purchase #7 $233.98   3.453%   $242.0593   $242.06   $242.05   $242.10  
  7 purchase totals = $933.83       $1,007.7738   $1,007.78   $1,007.85   $1,007.70