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 $107.86   13.692%   $122.6282   $122.63   $122.65   $122.60  
  Purchase #2 $225.33   6.254%   $239.4221   $239.42   $239.40   $239.40  
  Purchase #3 $50.35   12.496%   $56.6417   $56.64   $56.65   $56.60  
  Purchase #4 $95.96   5.670%   $101.4009   $101.40   $101.40   $101.40  
  Purchase #5 $196.69   9.527%   $215.4287   $215.43   $215.45   $215.40  
  Purchase #6 $49.30   3.158%   $50.8569   $50.86   $50.85   $50.90  
  Purchase #7 $227.64   13.607%   $258.615   $258.62   $258.60   $258.60  
  7 purchase totals = $953.13       $1,044.9935   $1,045.00   $1,045.00   $1,044.90