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	$240.99	3.452%	$249.309	$249.31	$249.30	$249.30
Purchase #2	$228.25	7.160%	$244.5927	$244.59	$244.60	$244.60
Purchase #3	$209.41	7.104%	$224.2865	$224.29	$224.30	$224.30
Purchase #4	$41.39	9.164%	$45.183	$45.18	$45.20	$45.20
Purchase #5	$112.38	7.277%	$120.5579	$120.56	$120.55	$120.60
Purchase #6	$130.29	7.790%	$140.4396	$140.44	$140.45	$140.40
Purchase #7	$90.42	9.521%	$99.0289	$99.03	$99.05	$99.00
7 purchase totals =	$1,053.13		$1,123.3976	$1,123.40	$1,123.45	$1,123.40