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 $218.67   13.835%   $248.923   $248.92   $248.90   $248.90  
  Purchase #2 $106.98   10.266%   $117.9626   $117.96   $117.95   $118.00  
  Purchase #3 $133.82   7.309%   $143.6009   $143.60   $143.60   $143.60  
  Purchase #4 $210.99   11.709%   $235.6948   $235.69   $235.70   $235.70  
  Purchase #5 $151.46   5.206%   $159.345   $159.35   $159.35   $159.30  
  Purchase #6 $216.25   3.842%   $224.5583   $224.56   $224.55   $224.60  
  Purchase #7 $61.63   13.445%   $69.9162   $69.92   $69.90   $69.90  
  7 purchase totals = $1,099.80       $1,200.0008   $1,200.00   $1,199.95   $1,200.00