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 $29.38   11.373%   $32.7214   $32.72   $32.70   $32.70  
  Purchase #2 $224.99   13.566%   $255.5121   $255.51   $255.50   $255.50  
  Purchase #3 $184.32   7.230%   $197.6463   $197.65   $197.65   $197.60  
  Purchase #4 $86.59   4.488%   $90.4762   $90.48   $90.50   $90.50  
  Purchase #5 $229.40   3.278%   $236.9197   $236.92   $236.90   $236.90  
  Purchase #6 $212.83   13.684%   $241.9537   $241.95   $241.95   $242.00  
  Purchase #7 $90.85   4.304%   $94.7602   $94.76   $94.75   $94.80  
  7 purchase totals = $1,058.36       $1,149.9896   $1,149.99   $1,149.95   $1,150.00