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	$73.41	10.148%	$80.8596	$80.86	$80.85	$80.90
Purchase #2	$166.54	12.312%	$187.0444	$187.04	$187.05	$187.00
Purchase #3	$195.86	5.631%	$206.8889	$206.89	$206.90	$206.90
Purchase #4	$180.66	8.825%	$196.6032	$196.60	$196.60	$196.60
Purchase #5	$40.64	4.374%	$42.4176	$42.42	$42.40	$42.40
Purchase #6	$172.82	3.172%	$178.3019	$178.30	$178.30	$178.30
Purchase #7	$122.79	4.493%	$128.307	$128.31	$128.30	$128.30
7 purchase totals =	$952.72		$1,020.4226	$1,020.42	$1,020.40	$1,020.40