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 $134.97   9.357%   $147.5991   $147.60   $147.60   $147.60  
  Purchase #2 $137.56   3.811%   $142.8024   $142.80   $142.80   $142.80  
  Purchase #3 $124.97   8.461%   $135.5437   $135.54   $135.55   $135.50  
  Purchase #4 $173.59   12.517%   $195.3183   $195.32   $195.30   $195.30  
  Purchase #5 $248.69   5.486%   $262.3331   $262.33   $262.35   $262.30  
  Purchase #6 $129.71   12.273%   $145.6293   $145.63   $145.65   $145.60  
  Purchase #7 $58.51   9.162%   $63.8707   $63.87   $63.85   $63.90  
  7 purchase totals = $1,008.00       $1,093.0966   $1,093.09   $1,093.10   $1,093.00