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	$237.71	8.259%	$257.3425	$257.34	$257.35	$257.30
Purchase #2	$117.27	6.333%	$124.6967	$124.70	$124.70	$124.70
Purchase #3	$66.46	11.526%	$74.1202	$74.12	$74.10	$74.10
Purchase #4	$173.61	13.130%	$196.405	$196.41	$196.40	$196.40
Purchase #5	$117.71	11.572%	$131.3314	$131.33	$131.35	$131.30
Purchase #6	$156.70	9.592%	$171.7307	$171.73	$171.75	$171.70
Purchase #7	$118.70	6.152%	$126.0024	$126.00	$126.00	$126.00
7 purchase totals =	$988.16		$1,081.6289	$1,081.63	$1,081.65	$1,081.50