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	$238.55	12.456%	$268.2638	$268.26	$268.25	$268.30
Purchase #2	$136.57	3.487%	$141.3322	$141.33	$141.35	$141.30
Purchase #3	$38.52	12.638%	$43.3882	$43.39	$43.40	$43.40
Purchase #4	$53.30	12.280%	$59.8452	$59.85	$59.85	$59.80
Purchase #5	$33.57	8.323%	$36.364	$36.36	$36.35	$36.40
Purchase #6	$21.61	10.443%	$23.8667	$23.87	$23.85	$23.90
Purchase #7	$149.27	11.608%	$166.5973	$166.60	$166.60	$166.60
7 purchase totals =	$671.39		$739.6574	$739.66	$739.65	$739.70