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	$51.39	6.859%	$54.9148	$54.91	$54.90	$54.90
Purchase #2	$223.79	13.186%	$253.2989	$253.30	$253.30	$253.30
Purchase #3	$115.45	10.460%	$127.5261	$127.53	$127.55	$127.50
Purchase #4	$135.54	11.283%	$150.833	$150.83	$150.85	$150.80
Purchase #5	$250.47	9.427%	$274.0818	$274.08	$274.10	$274.10
Purchase #6	$64.99	10.679%	$71.9303	$71.93	$71.95	$71.90
Purchase #7	$233.28	10.744%	$258.3436	$258.34	$258.35	$258.30
7 purchase totals =	$1,074.91		$1,190.9285	$1,190.92	$1,191.00	$1,190.80