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	$71.92	10.477%	$79.4551	$79.46	$79.45	$79.50
Purchase #2	$157.88	6.654%	$168.3853	$168.39	$168.40	$168.40
Purchase #3	$7.39	10.262%	$8.1484	$8.15	$8.15	$8.10
Purchase #4	$28.50	10.302%	$31.4361	$31.44	$31.45	$31.40
Purchase #5	$183.83	4.221%	$191.5895	$191.59	$191.60	$191.60
Purchase #6	$81.34	4.810%	$85.2525	$85.25	$85.25	$85.30
Purchase #7	$115.92	9.309%	$126.711	$126.71	$126.70	$126.70
7 purchase totals =	$646.78		$690.9779	$690.99	$691.00	$691.00