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	$159.43	7.459%	$171.3219	$171.32	$171.30	$171.30
Purchase #2	$239.28	12.406%	$268.9651	$268.97	$268.95	$269.00
Purchase #3	$83.46	6.771%	$89.1111	$89.11	$89.10	$89.10
Purchase #4	$197.55	5.123%	$207.6705	$207.67	$207.65	$207.70
Purchase #5	$63.72	10.650%	$70.5062	$70.51	$70.50	$70.50
Purchase #6	$133.46	3.309%	$137.8762	$137.88	$137.90	$137.90
Purchase #7	$54.94	11.300%	$61.1482	$61.15	$61.15	$61.10
7 purchase totals =	$931.84		$1,006.5992	$1,006.61	$1,006.55	$1,006.60