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	$54.90	5.513%	$57.9266	$57.93	$57.95	$57.90
Purchase #2	$230.52	12.453%	$259.2267	$259.23	$259.25	$259.20
Purchase #3	$94.70	10.544%	$104.6852	$104.69	$104.70	$104.70
Purchase #4	$59.78	4.543%	$62.4958	$62.50	$62.50	$62.50
Purchase #5	$232.49	5.733%	$245.8187	$245.82	$245.80	$245.80
Purchase #6	$39.57	7.573%	$42.5666	$42.57	$42.55	$42.60
Purchase #7	$168.89	6.858%	$180.4725	$180.47	$180.45	$180.50
7 purchase totals =	$880.85		$953.1921	$953.21	$953.20	$953.20