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	$64.92	12.543%	$73.0629	$73.06	$73.05	$73.10
Purchase #2	$33.26	12.680%	$37.4774	$37.48	$37.50	$37.50
Purchase #3	$196.60	11.589%	$219.384	$219.38	$219.40	$219.40
Purchase #4	$167.29	10.361%	$184.6229	$184.62	$184.60	$184.60
Purchase #5	$152.88	12.306%	$171.6934	$171.69	$171.70	$171.70
Purchase #6	$73.29	10.714%	$81.1423	$81.14	$81.15	$81.10
Purchase #7	$37.32	9.321%	$40.7986	$40.80	$40.80	$40.80
7 purchase totals =	$725.56		$808.1815	$808.17	$808.20	$808.20