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	$120.48	6.701%	$128.5534	$128.55	$128.55	$128.60
Purchase #2	$247.44	6.718%	$264.063	$264.06	$264.05	$264.10
Purchase #3	$125.92	8.354%	$136.4394	$136.44	$136.45	$136.40
Purchase #4	$159.72	3.839%	$165.8517	$165.85	$165.85	$165.90
Purchase #5	$78.28	3.589%	$81.0895	$81.09	$81.10	$81.10
Purchase #6	$66.27	10.622%	$73.3092	$73.31	$73.30	$73.30
Purchase #7	$146.98	6.457%	$156.4705	$156.47	$156.45	$156.50
7 purchase totals =	$945.09		$1,005.7767	$1,005.77	$1,005.75	$1,005.90