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	$63.36	5.839%	$67.0596	$67.06	$67.05	$67.10
Purchase #2	$90.35	6.599%	$96.3122	$96.31	$96.30	$96.30
Purchase #3	$242.48	4.609%	$253.6559	$253.66	$253.65	$253.70
Purchase #4	$103.41	9.376%	$113.1057	$113.11	$113.10	$113.10
Purchase #5	$73.68	6.659%	$78.5864	$78.59	$78.60	$78.60
Purchase #6	$76.62	13.442%	$86.9193	$86.92	$86.90	$86.90
Purchase #7	$135.67	10.622%	$150.0809	$150.08	$150.10	$150.10
7 purchase totals =	$785.57		$845.7200	$845.73	$845.70	$845.80