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	$67.73	6.492%	$72.127	$72.13	$72.15	$72.10
Purchase #2	$215.69	9.507%	$236.1956	$236.20	$236.20	$236.20
Purchase #3	$58.50	5.570%	$61.7585	$61.76	$61.75	$61.80
Purchase #4	$156.68	11.174%	$174.1874	$174.19	$174.20	$174.20
Purchase #5	$132.78	13.319%	$150.465	$150.47	$150.45	$150.50
Purchase #6	$142.61	11.444%	$158.9303	$158.93	$158.95	$158.90
Purchase #7	$111.75	8.200%	$120.9135	$120.91	$120.90	$120.90
7 purchase totals =	$885.74		$974.5773	$974.59	$974.60	$974.60