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 $245.49   9.478%   $268.7575   $268.76   $268.75   $268.80  
  Purchase #2 $153.26   8.604%   $166.4465   $166.45   $166.45   $166.40  
  Purchase #3 $214.47   9.523%   $234.894   $234.89   $234.90   $234.90  
  Purchase #4 $75.63   11.177%   $84.0832   $84.08   $84.10   $84.10  
  Purchase #5 $241.76   5.646%   $255.4098   $255.41   $255.40   $255.40  
  Purchase #6 $182.67   11.484%   $203.6478   $203.65   $203.65   $203.60  
  Purchase #7 $171.37   5.653%   $181.0575   $181.06   $181.05   $181.10  
  7 purchase totals = $1,284.65       $1,394.2963   $1,394.30   $1,394.30   $1,394.30