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	$174.96	13.830%	$199.157	$199.16	$199.15	$199.20
Purchase #2	$114.63	4.738%	$120.0612	$120.06	$120.05	$120.10
Purchase #3	$31.42	13.452%	$35.6466	$35.65	$35.65	$35.60
Purchase #4	$178.74	6.182%	$189.7897	$189.79	$189.80	$189.80
Purchase #5	$47.48	7.658%	$51.116	$51.12	$51.10	$51.10
Purchase #6	$111.32	7.371%	$119.5254	$119.53	$119.55	$119.50
Purchase #7	$96.31	9.529%	$105.4874	$105.49	$105.50	$105.50
7 purchase totals =	$754.86		$820.7833	$820.80	$820.80	$820.80