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	$176.30	6.536%	$187.823	$187.82	$187.80	$187.80
Purchase #2	$95.61	5.572%	$100.9374	$100.94	$100.95	$100.90
Purchase #3	$173.25	10.661%	$191.7202	$191.72	$191.70	$191.70
Purchase #4	$77.74	11.143%	$86.4026	$86.40	$86.40	$86.40
Purchase #5	$92.90	8.550%	$100.843	$100.84	$100.85	$100.80
Purchase #6	$180.76	7.811%	$194.8792	$194.88	$194.90	$194.90
Purchase #7	$22.70	13.313%	$25.7221	$25.72	$25.70	$25.70
7 purchase totals =	$819.26		$888.3275	$888.32	$888.30	$888.20