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	$247.92	11.856%	$277.3134	$277.31	$277.30	$277.30
Purchase #2	$51.83	4.868%	$54.3531	$54.35	$54.35	$54.40
Purchase #3	$216.30	12.524%	$243.3894	$243.39	$243.40	$243.40
Purchase #4	$223.33	6.845%	$238.6169	$238.62	$238.60	$238.60
Purchase #5	$190.38	12.269%	$213.7377	$213.74	$213.75	$213.70
Purchase #6	$72.31	13.399%	$81.9988	$82.00	$82.00	$82.00
Purchase #7	$106.25	13.315%	$120.3972	$120.40	$120.40	$120.40
7 purchase totals =	$1,108.32		$1,229.8065	$1,229.81	$1,229.80	$1,229.80