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	$88.63	12.845%	$100.0145	$100.01	$100.00	$100.00
Purchase #2	$25.74	11.554%	$28.714	$28.71	$28.70	$28.70
Purchase #3	$48.76	10.497%	$53.8783	$53.88	$53.90	$53.90
Purchase #4	$122.69	11.321%	$136.5797	$136.58	$136.60	$136.60
Purchase #5	$219.37	10.683%	$242.8053	$242.81	$242.80	$242.80
Purchase #6	$109.33	4.758%	$114.5319	$114.53	$114.55	$114.50
Purchase #7	$148.86	6.570%	$158.6401	$158.64	$158.65	$158.60
7 purchase totals =	$763.38		$835.1638	$835.16	$835.20	$835.10