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 $86.33   9.637%   $94.6496   $94.65   $94.65   $94.60  
  Purchase #2 $193.55   3.581%   $200.481   $200.48   $200.50   $200.50  
  Purchase #3 $246.69   5.705%   $260.7637   $260.76   $260.75   $260.80  
  Purchase #4 $250.91   5.647%   $265.0789   $265.08   $265.10   $265.10  
  Purchase #5 $86.99   5.481%   $91.7579   $91.76   $91.75   $91.80  
  Purchase #6 $162.57   3.161%   $167.7088   $167.71   $167.70   $167.70  
  Purchase #7 $182.37   4.314%   $190.2374   $190.24   $190.25   $190.20  
  7 purchase totals = $1,209.41       $1,270.6773   $1,270.68   $1,270.70   $1,270.70