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	$62.99	3.758%	$65.3572	$65.36	$65.35	$65.40
Purchase #2	$39.96	5.485%	$42.1518	$42.15	$42.15	$42.20
Purchase #3	$217.82	13.607%	$247.4588	$247.46	$247.45	$247.50
Purchase #4	$119.34	7.837%	$128.6927	$128.69	$128.70	$128.70
Purchase #5	$71.36	6.642%	$76.0997	$76.10	$76.10	$76.10
Purchase #6	$147.41	3.556%	$152.6519	$152.65	$152.65	$152.70
Purchase #7	$86.72	4.761%	$90.8487	$90.85	$90.85	$90.80
7 purchase totals =	$745.60		$803.2608	$803.26	$803.25	$803.40