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	$131.58	7.442%	$141.3722	$141.37	$141.35	$141.40
Purchase #2	$45.97	10.713%	$50.8948	$50.89	$50.90	$50.90
Purchase #3	$34.42	6.854%	$36.7791	$36.78	$36.80	$36.80
Purchase #4	$205.99	13.528%	$233.8563	$233.86	$233.85	$233.90
Purchase #5	$105.97	11.414%	$118.0654	$118.07	$118.05	$118.10
Purchase #6	$62.52	12.312%	$70.2175	$70.22	$70.20	$70.20
Purchase #7	$178.28	4.254%	$185.864	$185.86	$185.85	$185.90
7 purchase totals =	$764.73		$837.0493	$837.05	$837.00	$837.20