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	$238.39	7.337%	$255.8807	$255.88	$255.90	$255.90
Purchase #2	$73.49	8.387%	$79.6536	$79.65	$79.65	$79.70
Purchase #3	$225.93	10.578%	$249.8289	$249.83	$249.85	$249.80
Purchase #4	$40.31	13.108%	$45.5938	$45.59	$45.60	$45.60
Purchase #5	$245.26	9.800%	$269.2955	$269.30	$269.30	$269.30
Purchase #6	$148.92	5.722%	$157.4412	$157.44	$157.45	$157.40
Purchase #7	$65.86	12.280%	$73.9476	$73.95	$73.95	$73.90
7 purchase totals =	$1,038.16		$1,131.6413	$1,131.64	$1,131.70	$1,131.60