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	$123.44	11.194%	$137.2579	$137.26	$137.25	$137.30
Purchase #2	$172.74	10.399%	$190.7032	$190.70	$190.70	$190.70
Purchase #3	$98.77	11.295%	$109.9261	$109.93	$109.95	$109.90
Purchase #4	$171.99	6.584%	$183.3138	$183.31	$183.30	$183.30
Purchase #5	$56.57	5.204%	$59.5139	$59.51	$59.50	$59.50
Purchase #6	$146.48	5.872%	$155.0813	$155.08	$155.10	$155.10
Purchase #7	$202.87	12.800%	$228.8374	$228.84	$228.85	$228.80
7 purchase totals =	$972.86		$1,064.6336	$1,064.63	$1,064.65	$1,064.60