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	$125.41	3.871%	$130.2646	$130.26	$130.25	$130.30
Purchase #2	$80.89	5.481%	$85.3236	$85.32	$85.30	$85.30
Purchase #3	$6.39	13.692%	$7.2649	$7.26	$7.25	$7.30
Purchase #4	$163.91	9.179%	$178.9553	$178.96	$178.95	$179.00
Purchase #5	$91.84	13.169%	$103.9344	$103.93	$103.95	$103.90
Purchase #6	$238.73	13.704%	$271.4456	$271.45	$271.45	$271.40
Purchase #7	$94.84	6.272%	$100.7884	$100.79	$100.80	$100.80
7 purchase totals =	$802.01		$877.9768	$877.97	$877.95	$878.00