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	$132.68	6.172%	$140.869	$140.87	$140.85	$140.90
Purchase #2	$119.30	7.641%	$128.4157	$128.42	$128.40	$128.40
Purchase #3	$38.45	10.553%	$42.5076	$42.51	$42.50	$42.50
Purchase #4	$222.67	10.541%	$246.1416	$246.14	$246.15	$246.10
Purchase #5	$200.55	9.357%	$219.3155	$219.32	$219.30	$219.30
Purchase #6	$249.98	11.700%	$279.2277	$279.23	$279.25	$279.20
Purchase #7	$73.71	6.780%	$78.7075	$78.71	$78.70	$78.70
7 purchase totals =	$1,037.34		$1,135.1846	$1,135.20	$1,135.15	$1,135.10