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	$209.34	10.683%	$231.7038	$231.70	$231.70	$231.70
Purchase #2	$42.36	12.537%	$47.6707	$47.67	$47.65	$47.70
Purchase #3	$21.32	13.221%	$24.1387	$24.14	$24.15	$24.10
Purchase #4	$194.49	11.525%	$216.905	$216.91	$216.90	$216.90
Purchase #5	$185.25	3.608%	$191.9338	$191.93	$191.95	$191.90
Purchase #6	$208.82	9.806%	$229.2969	$229.30	$229.30	$229.30
Purchase #7	$80.88	10.261%	$89.1791	$89.18	$89.20	$89.20
7 purchase totals =	$942.46		$1,030.8280	$1,030.83	$1,030.85	$1,030.80