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	$228.31	12.228%	$256.2277	$256.23	$256.25	$256.20
Purchase #2	$213.32	10.244%	$235.1725	$235.17	$235.15	$235.20
Purchase #3	$227.57	6.758%	$242.9492	$242.95	$242.95	$242.90
Purchase #4	$128.88	11.360%	$143.5208	$143.52	$143.50	$143.50
Purchase #5	$97.66	6.336%	$103.8477	$103.85	$103.85	$103.80
Purchase #6	$31.69	11.565%	$35.3549	$35.35	$35.35	$35.40
Purchase #7	$58.42	8.338%	$63.2911	$63.29	$63.30	$63.30
7 purchase totals =	$985.85		$1,080.3639	$1,080.36	$1,080.35	$1,080.30