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	$5.89	7.514%	$6.3326	$6.33	$6.35	$6.30
Purchase #2	$150.91	12.322%	$169.5051	$169.51	$169.50	$169.50
Purchase #3	$188.83	5.631%	$199.463	$199.46	$199.45	$199.50
Purchase #4	$230.70	8.864%	$251.1492	$251.15	$251.15	$251.10
Purchase #5	$89.58	6.641%	$95.529	$95.53	$95.55	$95.50
Purchase #6	$184.78	8.632%	$200.7302	$200.73	$200.75	$200.70
Purchase #7	$140.51	11.122%	$156.1375	$156.14	$156.15	$156.10
7 purchase totals =	$991.20		$1,078.8466	$1,078.85	$1,078.90	$1,078.70