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 $101.49   12.329%   $114.0027   $114.00   $114.00   $114.00  
  Purchase #2 $31.51   3.378%   $32.5744   $32.57   $32.55   $32.60  
  Purchase #3 $118.72   3.466%   $122.8348   $122.83   $122.85   $122.80  
  Purchase #4 $104.35   3.331%   $107.8259   $107.83   $107.85   $107.80  
  Purchase #5 $245.94   4.692%   $257.4795   $257.48   $257.50   $257.50  
  Purchase #6 $8.30   12.527%   $9.3397   $9.34   $9.35   $9.30  
  Purchase #7 $134.45   10.684%   $148.8146   $148.81   $148.80   $148.80  
  7 purchase totals = $744.76       $792.8716   $792.86   $792.90   $792.80