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	$53.91	5.324%	$56.7802	$56.78	$56.80	$56.80
Purchase #2	$33.79	5.750%	$35.7329	$35.73	$35.75	$35.70
Purchase #3	$186.48	13.750%	$212.121	$212.12	$212.10	$212.10
Purchase #4	$249.39	10.591%	$275.8029	$275.80	$275.80	$275.80
Purchase #5	$129.40	9.293%	$141.4251	$141.43	$141.45	$141.40
Purchase #6	$195.76	13.677%	$222.5341	$222.53	$222.55	$222.50
Purchase #7	$133.65	6.244%	$141.9951	$142.00	$142.00	$142.00
7 purchase totals =	$982.38		$1,086.3913	$1,086.39	$1,086.45	$1,086.30