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	$170.59	7.346%	$183.1215	$183.12	$183.10	$183.10
Purchase #2	$238.61	10.871%	$264.5493	$264.55	$264.55	$264.50
Purchase #3	$170.46	4.483%	$178.1017	$178.10	$178.10	$178.10
Purchase #4	$133.75	12.630%	$150.6426	$150.64	$150.65	$150.60
Purchase #5	$138.84	11.579%	$154.9163	$154.92	$154.90	$154.90
Purchase #6	$73.92	11.666%	$82.5435	$82.54	$82.55	$82.50
Purchase #7	$89.35	5.515%	$94.2777	$94.28	$94.30	$94.30
7 purchase totals =	$1,015.52		$1,108.1526	$1,108.15	$1,108.15	$1,108.00