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	$97.58	6.485%	$103.9081	$103.91	$103.90	$103.90
Purchase #2	$83.86	7.191%	$89.8904	$89.89	$89.90	$89.90
Purchase #3	$228.48	6.158%	$242.5498	$242.55	$242.55	$242.50
Purchase #4	$215.42	7.312%	$231.1715	$231.17	$231.15	$231.20
Purchase #5	$105.35	5.464%	$111.1063	$111.11	$111.10	$111.10
Purchase #6	$75.98	12.568%	$85.5292	$85.53	$85.55	$85.50
Purchase #7	$112.85	11.297%	$125.5987	$125.60	$125.60	$125.60
7 purchase totals =	$919.52		$989.7540	$989.76	$989.75	$989.70