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	$171.92	6.515%	$183.1206	$183.12	$183.10	$183.10
Purchase #2	$247.71	13.214%	$280.4424	$280.44	$280.45	$280.40
Purchase #3	$172.62	12.460%	$194.1285	$194.13	$194.15	$194.10
Purchase #4	$95.81	3.174%	$98.851	$98.85	$98.85	$98.90
Purchase #5	$233.78	9.456%	$255.8862	$255.89	$255.90	$255.90
Purchase #6	$88.26	12.519%	$99.3093	$99.31	$99.30	$99.30
Purchase #7	$174.50	9.507%	$191.0897	$191.09	$191.10	$191.10
7 purchase totals =	$1,184.60		$1,302.8277	$1,302.83	$1,302.85	$1,302.80