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	$35.46	5.393%	$37.3724	$37.37	$37.35	$37.40
Purchase #2	$151.38	5.173%	$159.2109	$159.21	$159.20	$159.20
Purchase #3	$25.67	10.711%	$28.4195	$28.42	$28.40	$28.40
Purchase #4	$19.61	11.361%	$21.8379	$21.84	$21.85	$21.80
Purchase #5	$211.38	8.721%	$229.8144	$229.81	$229.80	$229.80
Purchase #6	$172.31	11.327%	$191.8276	$191.83	$191.85	$191.80
Purchase #7	$192.45	3.104%	$198.4236	$198.42	$198.40	$198.40
7 purchase totals =	$808.26		$866.9063	$866.90	$866.85	$866.80