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	$239.30	5.811%	$253.2057	$253.21	$253.20	$253.20
Purchase #2	$196.96	12.164%	$220.9182	$220.92	$220.90	$220.90
Purchase #3	$232.31	5.150%	$244.274	$244.27	$244.25	$244.30
Purchase #4	$77.63	6.157%	$82.4097	$82.41	$82.40	$82.40
Purchase #5	$245.62	13.725%	$279.3313	$279.33	$279.35	$279.30
Purchase #6	$91.57	8.609%	$99.4533	$99.45	$99.45	$99.50
Purchase #7	$39.93	13.866%	$45.4667	$45.47	$45.45	$45.50
7 purchase totals =	$1,123.32		$1,225.0589	$1,225.06	$1,225.00	$1,225.10