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	$223.71	11.401%	$249.2152	$249.22	$249.20	$249.20
Purchase #2	$159.56	12.431%	$179.3949	$179.39	$179.40	$179.40
Purchase #3	$82.89	9.593%	$90.8416	$90.84	$90.85	$90.80
Purchase #4	$30.80	7.696%	$33.1704	$33.17	$33.15	$33.20
Purchase #5	$209.99	3.109%	$216.5186	$216.52	$216.50	$216.50
Purchase #6	$238.27	5.257%	$250.7959	$250.80	$250.80	$250.80
Purchase #7	$121.59	10.648%	$134.5369	$134.54	$134.55	$134.50
7 purchase totals =	$1,066.81		$1,154.4735	$1,154.48	$1,154.45	$1,154.40