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	$42.64	13.840%	$48.5414	$48.54	$48.55	$48.50
Purchase #2	$20.99	3.802%	$21.788	$21.79	$21.80	$21.80
Purchase #3	$25.76	11.514%	$28.726	$28.73	$28.75	$28.70
Purchase #4	$53.66	6.540%	$57.1694	$57.17	$57.15	$57.20
Purchase #5	$213.42	4.450%	$222.9172	$222.92	$222.90	$222.90
Purchase #6	$141.72	10.598%	$156.7395	$156.74	$156.75	$156.70
Purchase #7	$52.94	5.290%	$55.7405	$55.74	$55.75	$55.70
7 purchase totals =	$551.13		$591.6220	$591.63	$591.65	$591.50