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	$180.32	8.824%	$196.2314	$196.23	$196.25	$196.20
Purchase #2	$245.80	13.702%	$279.4795	$279.48	$279.50	$279.50
Purchase #3	$103.38	5.700%	$109.2727	$109.27	$109.25	$109.30
Purchase #4	$146.70	6.726%	$156.567	$156.57	$156.55	$156.60
Purchase #5	$156.54	5.489%	$165.1325	$165.13	$165.15	$165.10
Purchase #6	$37.92	9.139%	$41.3855	$41.39	$41.40	$41.40
Purchase #7	$247.71	6.435%	$263.6501	$263.65	$263.65	$263.70
7 purchase totals =	$1,118.37		$1,211.7187	$1,211.72	$1,211.75	$1,211.80