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	$122.88	8.220%	$132.9807	$132.98	$133.00	$133.00
Purchase #2	$60.98	3.653%	$63.2076	$63.21	$63.20	$63.20
Purchase #3	$26.74	5.862%	$28.3075	$28.31	$28.30	$28.30
Purchase #4	$89.43	12.774%	$100.8538	$100.85	$100.85	$100.90
Purchase #5	$26.38	9.514%	$28.8898	$28.89	$28.90	$28.90
Purchase #6	$42.32	3.690%	$43.8816	$43.88	$43.90	$43.90
Purchase #7	$142.76	5.135%	$150.0907	$150.09	$150.10	$150.10
7 purchase totals =	$511.49		$548.2117	$548.21	$548.25	$548.30