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	$49.87	6.432%	$53.0776	$53.08	$53.10	$53.10
Purchase #2	$94.54	5.616%	$99.8494	$99.85	$99.85	$99.80
Purchase #3	$131.63	4.757%	$137.8916	$137.89	$137.90	$137.90
Purchase #4	$104.26	6.444%	$110.9785	$110.98	$111.00	$111.00
Purchase #5	$45.35	10.821%	$50.2573	$50.26	$50.25	$50.30
Purchase #6	$73.89	4.451%	$77.1788	$77.18	$77.20	$77.20
Purchase #7	$65.62	5.155%	$69.0027	$69.00	$69.00	$69.00
7 purchase totals =	$565.16		$598.2359	$598.24	$598.30	$598.30