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	$28.69	12.134%	$32.1712	$32.17	$32.15	$32.20
Purchase #2	$123.84	6.310%	$131.6543	$131.65	$131.65	$131.70
Purchase #3	$56.77	7.439%	$60.9931	$60.99	$61.00	$61.00
Purchase #4	$217.27	8.372%	$235.4598	$235.46	$235.45	$235.50
Purchase #5	$80.76	6.325%	$85.8681	$85.87	$85.85	$85.90
Purchase #6	$168.94	13.581%	$191.8837	$191.88	$191.90	$191.90
Purchase #7	$110.66	6.850%	$118.2402	$118.24	$118.25	$118.20
7 purchase totals =	$786.93		$856.2704	$856.26	$856.25	$856.40