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	$28.58	11.758%	$31.9404	$31.94	$31.95	$31.90
Purchase #2	$213.58	4.522%	$223.2381	$223.24	$223.25	$223.20
Purchase #3	$246.28	8.705%	$267.7187	$267.72	$267.70	$267.70
Purchase #4	$67.53	10.705%	$74.7591	$74.76	$74.75	$74.80
Purchase #5	$165.31	8.229%	$178.9134	$178.91	$178.90	$178.90
Purchase #6	$45.50	5.804%	$48.1408	$48.14	$48.15	$48.10
Purchase #7	$228.81	6.575%	$243.8543	$243.85	$243.85	$243.90
7 purchase totals =	$995.59		$1,068.5648	$1,068.56	$1,068.55	$1,068.50