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	$44.92	13.186%	$50.8432	$50.84	$50.85	$50.80
Purchase #2	$233.46	4.492%	$243.947	$243.95	$243.95	$243.90
Purchase #3	$84.97	9.501%	$93.043	$93.04	$93.05	$93.00
Purchase #4	$198.42	7.109%	$212.5257	$212.53	$212.55	$212.50
Purchase #5	$161.72	12.854%	$182.5075	$182.51	$182.50	$182.50
Purchase #6	$71.92	8.673%	$78.1576	$78.16	$78.15	$78.20
Purchase #7	$173.86	6.777%	$185.6425	$185.64	$185.65	$185.60
7 purchase totals =	$969.27		$1,046.6665	$1,046.67	$1,046.70	$1,046.50