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	$173.89	6.789%	$185.6954	$185.70	$185.70	$185.70
Purchase #2	$135.27	4.467%	$141.3125	$141.31	$141.30	$141.30
Purchase #3	$184.26	11.197%	$204.8916	$204.89	$204.90	$204.90
Purchase #4	$38.30	7.313%	$41.1009	$41.10	$41.10	$41.10
Purchase #5	$212.48	11.348%	$236.5922	$236.59	$236.60	$236.60
Purchase #6	$222.84	8.293%	$241.3201	$241.32	$241.30	$241.30
Purchase #7	$29.86	13.138%	$33.783	$33.78	$33.80	$33.80
7 purchase totals =	$996.90		$1,084.6957	$1,084.69	$1,084.70	$1,084.70