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 $201.37   5.726%   $212.9004   $212.90   $212.90   $212.90  
  Purchase #2 $188.96   13.584%   $214.6283   $214.63   $214.65   $214.60  
  Purchase #3 $65.37   7.394%   $70.2035   $70.20   $70.20   $70.20  
  Purchase #4 $234.52   9.851%   $257.6226   $257.62   $257.60   $257.60  
  Purchase #5 $116.72   4.874%   $122.4089   $122.41   $122.40   $122.40  
  Purchase #6 $35.88   12.114%   $40.2265   $40.23   $40.25   $40.20  
  Purchase #7 $114.48   11.233%   $127.3395   $127.34   $127.35   $127.30  
  7 purchase totals = $957.30       $1,045.3297   $1,045.33   $1,045.35   $1,045.20