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 $34.27   11.556%   $38.2302   $38.23   $38.25   $38.20  
  Purchase #2 $152.98   13.269%   $173.2789   $173.28   $173.30   $173.30  
  Purchase #3 $174.86   5.183%   $183.923   $183.92   $183.90   $183.90  
  Purchase #4 $229.77   7.155%   $246.21   $246.21   $246.20   $246.20  
  Purchase #5 $132.76   12.427%   $149.2581   $149.26   $149.25   $149.30  
  Purchase #6 $203.71   13.391%   $230.9888   $230.99   $231.00   $231.00  
  Purchase #7 $205.57   13.565%   $233.4556   $233.46   $233.45   $233.50  
  7 purchase totals = $1,133.92       $1,255.3446   $1,255.35   $1,255.35   $1,255.40