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	$93.59	7.791%	$100.8816	$100.88	$100.90	$100.90
Purchase #2	$247.69	11.240%	$275.5304	$275.53	$275.55	$275.50
Purchase #3	$79.78	3.563%	$82.6226	$82.62	$82.60	$82.60
Purchase #4	$54.94	5.130%	$57.7584	$57.76	$57.75	$57.80
Purchase #5	$53.46	10.350%	$58.9931	$58.99	$59.00	$59.00
Purchase #6	$107.84	4.157%	$112.3229	$112.32	$112.30	$112.30
Purchase #7	$250.36	3.843%	$259.9813	$259.98	$260.00	$260.00
7 purchase totals =	$887.66		$948.0903	$948.08	$948.10	$948.10