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	$72.31	7.757%	$77.9191	$77.92	$77.90	$77.90
Purchase #2	$250.88	8.110%	$271.2264	$271.23	$271.25	$271.20
Purchase #3	$97.69	7.654%	$105.1672	$105.17	$105.15	$105.20
Purchase #4	$111.57	13.605%	$126.7491	$126.75	$126.75	$126.70
Purchase #5	$40.31	5.105%	$42.3678	$42.37	$42.35	$42.40
Purchase #6	$6.92	13.615%	$7.8622	$7.86	$7.85	$7.90
Purchase #7	$211.94	6.483%	$225.6801	$225.68	$225.70	$225.70
7 purchase totals =	$791.62		$856.9719	$856.98	$856.95	$857.00