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	$56.43	9.719%	$61.9144	$61.91	$61.90	$61.90
Purchase #2	$51.53	8.710%	$56.0183	$56.02	$56.00	$56.00
Purchase #3	$202.76	4.431%	$211.7443	$211.74	$211.75	$211.70
Purchase #4	$63.33	4.554%	$66.214	$66.21	$66.20	$66.20
Purchase #5	$159.33	6.672%	$169.9605	$169.96	$169.95	$170.00
Purchase #6	$83.98	6.668%	$89.5798	$89.58	$89.60	$89.60
Purchase #7	$151.89	12.708%	$171.1922	$171.19	$171.20	$171.20
7 purchase totals =	$769.25		$826.6235	$826.61	$826.60	$826.60