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	$98.61	6.335%	$104.8569	$104.86	$104.85	$104.90
Purchase #2	$152.64	3.512%	$158.0007	$158.00	$158.00	$158.00
Purchase #3	$150.86	3.625%	$156.3287	$156.33	$156.35	$156.30
Purchase #4	$81.71	4.116%	$85.0732	$85.07	$85.05	$85.10
Purchase #5	$244.92	5.306%	$257.9155	$257.92	$257.90	$257.90
Purchase #6	$80.35	6.687%	$85.723	$85.72	$85.70	$85.70
Purchase #7	$39.30	8.171%	$42.5112	$42.51	$42.50	$42.50
7 purchase totals =	$848.39		$890.4092	$890.41	$890.35	$890.40