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	$55.55	6.278%	$59.0374	$59.04	$59.05	$59.00
Purchase #2	$127.62	10.629%	$141.1847	$141.18	$141.20	$141.20
Purchase #3	$232.89	7.372%	$250.0587	$250.06	$250.05	$250.10
Purchase #4	$133.75	10.183%	$147.3698	$147.37	$147.35	$147.40
Purchase #5	$31.95	10.353%	$35.2578	$35.26	$35.25	$35.30
Purchase #6	$61.60	6.796%	$65.7863	$65.79	$65.80	$65.80
Purchase #7	$65.70	8.637%	$71.3745	$71.37	$71.35	$71.40
7 purchase totals =	$709.06		$770.0692	$770.07	$770.05	$770.20