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	$104.54	6.554%	$111.3916	$111.39	$111.40	$111.40
Purchase #2	$187.46	13.216%	$212.2347	$212.23	$212.25	$212.20
Purchase #3	$140.43	13.251%	$159.0384	$159.04	$159.05	$159.00
Purchase #4	$37.60	13.696%	$42.7497	$42.75	$42.75	$42.70
Purchase #5	$158.81	8.278%	$171.9563	$171.96	$171.95	$172.00
Purchase #6	$210.65	12.638%	$237.2719	$237.27	$237.25	$237.30
Purchase #7	$45.78	11.600%	$51.0905	$51.09	$51.10	$51.10
7 purchase totals =	$885.27		$985.7331	$985.73	$985.75	$985.70