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 $243.25   13.548%   $276.2055   $276.21   $276.20   $276.20  
  Purchase #2 $203.79   6.856%   $217.7618   $217.76   $217.75   $217.80  
  Purchase #3 $62.60   3.647%   $64.883   $64.88   $64.90   $64.90  
  Purchase #4 $13.67   10.125%   $15.0541   $15.05   $15.05   $15.10  
  Purchase #5 $191.85   12.339%   $215.5224   $215.52   $215.50   $215.50  
  Purchase #6 $24.85   10.492%   $27.4573   $27.46   $27.45   $27.50  
  Purchase #7 $157.39   7.599%   $169.3501   $169.35   $169.35   $169.40  
  7 purchase totals = $897.40       $986.2342   $986.23   $986.20   $986.40