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	$82.74	9.299%	$90.434	$90.43	$90.45	$90.40
Purchase #2	$76.86	11.495%	$85.6951	$85.70	$85.70	$85.70
Purchase #3	$65.53	10.417%	$72.3563	$72.36	$72.35	$72.40
Purchase #4	$213.67	6.537%	$227.6376	$227.64	$227.65	$227.60
Purchase #5	$226.29	7.187%	$242.5535	$242.55	$242.55	$242.60
Purchase #6	$48.76	9.344%	$53.3161	$53.32	$53.30	$53.30
Purchase #7	$98.34	7.406%	$105.6231	$105.62	$105.60	$105.60
7 purchase totals =	$812.19		$877.6157	$877.62	$877.60	$877.60