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	$71.74	9.169%	$78.3178	$78.32	$78.30	$78.30
Purchase #2	$142.32	10.524%	$157.2978	$157.30	$157.30	$157.30
Purchase #3	$66.98	8.459%	$72.6458	$72.65	$72.65	$72.60
Purchase #4	$174.66	5.118%	$183.5991	$183.60	$183.60	$183.60
Purchase #5	$169.32	11.204%	$188.2906	$188.29	$188.30	$188.30
Purchase #6	$60.76	8.468%	$65.9052	$65.91	$65.90	$65.90
Purchase #7	$181.58	4.361%	$189.4987	$189.50	$189.50	$189.50
7 purchase totals =	$867.36		$935.5550	$935.57	$935.55	$935.50