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	$69.59	12.698%	$78.4265	$78.43	$78.45	$78.40
Purchase #2	$37.73	11.564%	$42.0931	$42.09	$42.10	$42.10
Purchase #3	$159.67	5.363%	$168.2331	$168.23	$168.25	$168.20
Purchase #4	$48.92	5.868%	$51.7906	$51.79	$51.80	$51.80
Purchase #5	$56.40	9.583%	$61.8048	$61.80	$61.80	$61.80
Purchase #6	$150.73	13.379%	$170.8962	$170.90	$170.90	$170.90
Purchase #7	$28.61	5.399%	$30.1547	$30.15	$30.15	$30.20
7 purchase totals =	$551.65		$603.3990	$603.39	$603.45	$603.40