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 $119.92   3.213%   $123.773   $123.77   $123.75   $123.80  
  Purchase #2 $75.44   5.178%   $79.3463   $79.35   $79.35   $79.30  
  Purchase #3 $167.59   12.747%   $188.9527   $188.95   $188.95   $189.00  
  Purchase #4 $71.76   13.513%   $81.4569   $81.46   $81.45   $81.50  
  Purchase #5 $63.74   7.364%   $68.4338   $68.43   $68.45   $68.40  
  Purchase #6 $216.99   11.190%   $241.2712   $241.27   $241.25   $241.30  
  Purchase #7 $229.88   4.574%   $240.3947   $240.39   $240.40   $240.40  
  7 purchase totals = $945.32       $1,023.6286   $1,023.62   $1,023.60   $1,023.70