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 $208.30   12.656%   $234.6624   $234.66   $234.65   $234.70  
  Purchase #2 $250.90   6.361%   $266.8597   $266.86   $266.85   $266.90  
  Purchase #3 $28.54   5.843%   $30.2076   $30.21   $30.20   $30.20  
  Purchase #4 $107.29   13.736%   $122.0274   $122.03   $122.05   $122.00  
  Purchase #5 $57.82   6.503%   $61.58   $61.58   $61.60   $61.60  
  Purchase #6 $171.90   11.713%   $192.0346   $192.03   $192.05   $192.00  
  Purchase #7 $116.60   13.685%   $132.5567   $132.56   $132.55   $132.60  
  7 purchase totals = $941.35       $1,039.9284   $1,039.93   $1,039.95   $1,040.00