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	$136.70	10.298%	$150.7774	$150.78	$150.80	$150.80
Purchase #2	$38.56	5.390%	$40.6384	$40.64	$40.65	$40.60
Purchase #3	$84.44	9.157%	$92.1722	$92.17	$92.15	$92.20
Purchase #4	$225.88	3.183%	$233.0698	$233.07	$233.05	$233.10
Purchase #5	$189.90	5.765%	$200.8477	$200.85	$200.85	$200.80
Purchase #6	$151.61	3.103%	$156.3145	$156.31	$156.30	$156.30
Purchase #7	$77.91	9.170%	$85.0543	$85.05	$85.05	$85.10
7 purchase totals =	$905.00		$958.8743	$958.87	$958.85	$958.90