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	$40.39	5.224%	$42.5	$42.50	$42.50	$42.50
Purchase #2	$184.59	9.633%	$202.3716	$202.37	$202.35	$202.40
Purchase #3	$51.65	9.395%	$56.5025	$56.50	$56.50	$56.50
Purchase #4	$52.85	6.473%	$56.271	$56.27	$56.25	$56.30
Purchase #5	$233.96	3.201%	$241.4491	$241.45	$241.45	$241.40
Purchase #6	$53.98	13.672%	$61.3601	$61.36	$61.35	$61.40
Purchase #7	$101.89	11.158%	$113.2589	$113.26	$113.25	$113.30
7 purchase totals =	$719.31		$773.7132	$773.71	$773.65	$773.80