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	$107.82	9.693%	$118.271	$118.27	$118.25	$118.30
Purchase #2	$195.48	3.475%	$202.2729	$202.27	$202.25	$202.30
Purchase #3	$28.73	4.170%	$29.928	$29.93	$29.95	$29.90
Purchase #4	$16.31	13.131%	$18.4517	$18.45	$18.45	$18.50
Purchase #5	$147.32	12.758%	$166.1151	$166.12	$166.10	$166.10
Purchase #6	$172.47	13.849%	$196.3554	$196.36	$196.35	$196.40
Purchase #7	$85.76	7.156%	$91.897	$91.90	$91.90	$91.90
7 purchase totals =	$753.89		$823.2911	$823.30	$823.25	$823.40