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	$18.66	10.666%	$20.6503	$20.65	$20.65	$20.70
Purchase #2	$147.53	9.457%	$161.4819	$161.48	$161.50	$161.50
Purchase #3	$11.63	6.467%	$12.3821	$12.38	$12.40	$12.40
Purchase #4	$54.76	5.719%	$57.8917	$57.89	$57.90	$57.90
Purchase #5	$25.46	6.348%	$27.0762	$27.08	$27.10	$27.10
Purchase #6	$128.84	8.322%	$139.5621	$139.56	$139.55	$139.60
Purchase #7	$214.88	6.503%	$228.8536	$228.85	$228.85	$228.90
7 purchase totals =	$601.76		$647.8979	$647.89	$647.95	$648.10