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	$84.77	6.298%	$90.1088	$90.11	$90.10	$90.10
Purchase #2	$120.46	13.719%	$136.9859	$136.99	$137.00	$137.00
Purchase #3	$69.65	12.630%	$78.4468	$78.45	$78.45	$78.40
Purchase #4	$132.73	12.755%	$149.6597	$149.66	$149.65	$149.70
Purchase #5	$128.34	12.839%	$144.8176	$144.82	$144.80	$144.80
Purchase #6	$64.70	13.661%	$73.5387	$73.54	$73.55	$73.50
Purchase #7	$60.29	4.702%	$63.1248	$63.12	$63.10	$63.10
7 purchase totals =	$660.94		$736.6823	$736.69	$736.65	$736.60