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	$174.51	3.235%	$180.1554	$180.16	$180.15	$180.20
Purchase #2	$165.77	13.701%	$188.4821	$188.48	$188.50	$188.50
Purchase #3	$136.51	13.456%	$154.8788	$154.88	$154.90	$154.90
Purchase #4	$48.39	12.582%	$54.4784	$54.48	$54.50	$54.50
Purchase #5	$37.34	6.248%	$39.673	$39.67	$39.65	$39.70
Purchase #6	$223.30	7.574%	$240.2127	$240.21	$240.20	$240.20
Purchase #7	$113.67	6.199%	$120.7164	$120.72	$120.70	$120.70
7 purchase totals =	$899.49		$978.5968	$978.60	$978.60	$978.70