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	$53.97	5.792%	$57.0959	$57.10	$57.10	$57.10
Purchase #2	$136.68	13.823%	$155.5733	$155.57	$155.55	$155.60
Purchase #3	$103.32	4.386%	$107.8516	$107.85	$107.85	$107.90
Purchase #4	$225.59	8.736%	$245.2975	$245.30	$245.30	$245.30
Purchase #5	$80.85	3.271%	$83.4946	$83.49	$83.50	$83.50
Purchase #6	$59.82	8.204%	$64.7276	$64.73	$64.75	$64.70
Purchase #7	$96.82	3.825%	$100.5234	$100.52	$100.50	$100.50
7 purchase totals =	$757.05		$814.5639	$814.56	$814.55	$814.60