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 $105.77   10.581%   $116.9615   $116.96   $116.95   $117.00  
  Purchase #2 $206.26   13.625%   $234.3629   $234.36   $234.35   $234.40  
  Purchase #3 $142.77   13.568%   $162.141   $162.14   $162.15   $162.10  
  Purchase #4 $172.57   9.322%   $188.657   $188.66   $188.65   $188.70  
  Purchase #5 $138.28   4.483%   $144.4791   $144.48   $144.50   $144.50  
  Purchase #6 $182.54   3.147%   $188.2845   $188.28   $188.30   $188.30  
  Purchase #7 $210.80   9.747%   $231.3467   $231.35   $231.35   $231.30  
  7 purchase totals = $1,158.99       $1,266.2327   $1,266.23   $1,266.25   $1,266.30