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	$93.40	6.593%	$99.5579	$99.56	$99.55	$99.60
Purchase #2	$147.63	7.198%	$158.2564	$158.26	$158.25	$158.30
Purchase #3	$216.57	8.798%	$235.6238	$235.62	$235.60	$235.60
Purchase #4	$98.31	10.652%	$108.782	$108.78	$108.80	$108.80
Purchase #5	$77.54	11.237%	$86.2532	$86.25	$86.25	$86.30
Purchase #6	$108.93	8.571%	$118.2664	$118.27	$118.25	$118.30
Purchase #7	$235.73	10.277%	$259.956	$259.96	$259.95	$260.00
7 purchase totals =	$978.11		$1,066.6957	$1,066.70	$1,066.65	$1,066.90