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 $68.54   7.720%   $73.8313   $73.83   $73.85   $73.80  
  Purchase #2 $98.59   11.719%   $110.1438   $110.14   $110.15   $110.10  
  Purchase #3 $79.26   9.137%   $86.502   $86.50   $86.50   $86.50  
  Purchase #4 $236.96   9.129%   $258.5921   $258.59   $258.60   $258.60  
  Purchase #5 $115.99   7.665%   $124.8806   $124.88   $124.90   $124.90  
  Purchase #6 $107.30   10.762%   $118.8476   $118.85   $118.85   $118.80  
  Purchase #7 $116.52   8.426%   $126.338   $126.34   $126.35   $126.30  
  7 purchase totals = $823.16       $899.1354   $899.13   $899.20   $899.00