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	$6.94	13.629%	$7.8859	$7.89	$7.90	$7.90
Purchase #2	$80.55	13.770%	$91.6417	$91.64	$91.65	$91.60
Purchase #3	$170.73	5.521%	$180.156	$180.16	$180.15	$180.20
Purchase #4	$36.48	10.537%	$40.3239	$40.32	$40.30	$40.30
Purchase #5	$9.82	10.179%	$10.8196	$10.82	$10.80	$10.80
Purchase #6	$114.33	3.194%	$117.9817	$117.98	$118.00	$118.00
Purchase #7	$31.54	13.429%	$35.7755	$35.78	$35.80	$35.80
7 purchase totals =	$450.39		$484.5843	$484.59	$484.60	$484.60