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	$70.39	3.407%	$72.7882	$72.79	$72.80	$72.80
Purchase #2	$149.46	8.533%	$162.2134	$162.21	$162.20	$162.20
Purchase #3	$246.86	9.825%	$271.114	$271.11	$271.10	$271.10
Purchase #4	$206.44	10.695%	$228.5188	$228.52	$228.50	$228.50
Purchase #5	$242.89	9.399%	$265.7192	$265.72	$265.70	$265.70
Purchase #6	$78.49	13.814%	$89.3326	$89.33	$89.35	$89.30
Purchase #7	$79.94	3.495%	$82.7339	$82.73	$82.75	$82.70
7 purchase totals =	$1,074.47		$1,172.4201	$1,172.41	$1,172.40	$1,172.30