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 $134.79   5.304%   $141.9393   $141.94   $141.95   $141.90  
  Purchase #2 $38.63   5.520%   $40.7624   $40.76   $40.75   $40.80  
  Purchase #3 $122.76   5.835%   $129.923   $129.92   $129.90   $129.90  
  Purchase #4 $38.48   5.714%   $40.6787   $40.68   $40.70   $40.70  
  Purchase #5 $55.72   11.116%   $61.9138   $61.91   $61.90   $61.90  
  Purchase #6 $16.32   11.583%   $18.2103   $18.21   $18.20   $18.20  
  Purchase #7 $150.35   6.607%   $160.2836   $160.28   $160.30   $160.30  
  7 purchase totals = $557.05       $593.7111   $593.70   $593.70   $593.70