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 $236.74   10.274%   $261.0627   $261.06   $261.05   $261.10  
  Purchase #2 $14.78   12.172%   $16.579   $16.58   $16.60   $16.60  
  Purchase #3 $209.78   4.481%   $219.1802   $219.18   $219.20   $219.20  
  Purchase #4 $226.80   6.668%   $241.923   $241.92   $241.90   $241.90  
  Purchase #5 $58.28   12.127%   $65.3476   $65.35   $65.35   $65.30  
  Purchase #6 $239.35   5.550%   $252.6339   $252.63   $252.65   $252.60  
  Purchase #7 $42.77   12.228%   $47.9999   $48.00   $48.00   $48.00  
  7 purchase totals = $1,028.50       $1,104.7263   $1,104.72   $1,104.75   $1,104.70