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	$77.36	4.728%	$81.0176	$81.02	$81.00	$81.00
Purchase #2	$78.72	13.615%	$89.4377	$89.44	$89.45	$89.40
Purchase #3	$195.53	10.425%	$215.914	$215.91	$215.90	$215.90
Purchase #4	$28.43	7.316%	$30.5099	$30.51	$30.50	$30.50
Purchase #5	$171.54	5.316%	$180.6591	$180.66	$180.65	$180.70
Purchase #6	$240.39	12.171%	$269.6479	$269.65	$269.65	$269.60
Purchase #7	$42.65	9.235%	$46.5887	$46.59	$46.60	$46.60
7 purchase totals =	$834.62		$913.7749	$913.78	$913.75	$913.70