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	$152.84	10.519%	$168.9172	$168.92	$168.90	$168.90
Purchase #2	$45.81	5.711%	$48.4262	$48.43	$48.45	$48.40
Purchase #3	$103.64	5.714%	$109.562	$109.56	$109.55	$109.60
Purchase #4	$40.82	3.363%	$42.1928	$42.19	$42.20	$42.20
Purchase #5	$34.54	12.563%	$38.8793	$38.88	$38.90	$38.90
Purchase #6	$242.82	13.454%	$275.489	$275.49	$275.50	$275.50
Purchase #7	$23.28	12.530%	$26.197	$26.20	$26.20	$26.20
7 purchase totals =	$643.75		$709.6635	$709.67	$709.70	$709.70