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 $239.97   9.709%   $263.2687   $263.27   $263.25   $263.30  
  Purchase #2 $117.53   8.574%   $127.607   $127.61   $127.60   $127.60  
  Purchase #3 $208.69   10.697%   $231.0136   $231.01   $231.00   $231.00  
  Purchase #4 $20.78   5.112%   $21.8423   $21.84   $21.85   $21.80  
  Purchase #5 $247.77   12.412%   $278.5232   $278.52   $278.50   $278.50  
  Purchase #6 $180.88   13.618%   $205.5122   $205.51   $205.50   $205.50  
  Purchase #7 $65.99   3.370%   $68.2139   $68.21   $68.20   $68.20  
  7 purchase totals = $1,081.61       $1,195.9809   $1,195.97   $1,195.90   $1,195.90