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	$54.70	5.147%	$57.5154	$57.52	$57.50	$57.50
Purchase #2	$196.75	4.872%	$206.3357	$206.34	$206.35	$206.30
Purchase #3	$94.33	11.739%	$105.4034	$105.40	$105.40	$105.40
Purchase #4	$207.74	3.179%	$214.3441	$214.34	$214.35	$214.30
Purchase #5	$187.46	3.529%	$194.0755	$194.08	$194.10	$194.10
Purchase #6	$85.54	3.457%	$88.4971	$88.50	$88.50	$88.50
Purchase #7	$81.61	10.456%	$90.1431	$90.14	$90.15	$90.10
7 purchase totals =	$908.13		$956.3143	$956.32	$956.35	$956.20