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	$75.41	4.580%	$78.8638	$78.86	$78.85	$78.90
Purchase #2	$67.33	7.405%	$72.3158	$72.32	$72.30	$72.30
Purchase #3	$32.37	11.865%	$36.2107	$36.21	$36.20	$36.20
Purchase #4	$21.33	6.352%	$22.6849	$22.68	$22.70	$22.70
Purchase #5	$118.68	4.771%	$124.3422	$124.34	$124.35	$124.30
Purchase #6	$50.26	3.332%	$51.9347	$51.93	$51.95	$51.90
Purchase #7	$65.50	10.457%	$72.3493	$72.35	$72.35	$72.30
7 purchase totals =	$430.88		$458.7014	$458.69	$458.70	$458.60