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	$127.35	7.849%	$137.3457	$137.35	$137.35	$137.30
Purchase #2	$243.72	10.271%	$268.7525	$268.75	$268.75	$268.80
Purchase #3	$72.80	10.635%	$80.5423	$80.54	$80.55	$80.50
Purchase #4	$93.50	3.575%	$96.8426	$96.84	$96.85	$96.80
Purchase #5	$35.51	5.476%	$37.4545	$37.45	$37.45	$37.50
Purchase #6	$193.42	9.532%	$211.8568	$211.86	$211.85	$211.90
Purchase #7	$244.72	8.271%	$264.9608	$264.96	$264.95	$265.00
7 purchase totals =	$1,011.02		$1,097.7552	$1,097.75	$1,097.75	$1,097.80