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	$250.52	8.489%	$271.7866	$271.79	$271.80	$271.80
Purchase #2	$86.34	11.633%	$96.3839	$96.38	$96.40	$96.40
Purchase #3	$48.33	8.338%	$52.3598	$52.36	$52.35	$52.40
Purchase #4	$183.48	3.819%	$190.4871	$190.49	$190.50	$190.50
Purchase #5	$66.82	10.275%	$73.6858	$73.69	$73.70	$73.70
Purchase #6	$198.39	3.252%	$204.8416	$204.84	$204.85	$204.80
Purchase #7	$171.52	11.541%	$191.3151	$191.32	$191.30	$191.30
7 purchase totals =	$1,005.40		$1,080.8599	$1,080.87	$1,080.90	$1,080.90