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	$45.28	13.527%	$51.405	$51.41	$51.40	$51.40
Purchase #2	$171.54	9.739%	$188.2463	$188.25	$188.25	$188.20
Purchase #3	$206.62	3.221%	$213.2752	$213.28	$213.30	$213.30
Purchase #4	$92.29	12.430%	$103.7616	$103.76	$103.75	$103.80
Purchase #5	$79.71	13.769%	$90.6853	$90.69	$90.70	$90.70
Purchase #6	$127.39	9.227%	$139.1443	$139.14	$139.15	$139.10
Purchase #7	$17.90	11.322%	$19.9266	$19.93	$19.95	$19.90
7 purchase totals =	$740.73		$806.4443	$806.46	$806.50	$806.40