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	$29.76	6.182%	$31.5998	$31.60	$31.60	$31.60
Purchase #2	$56.84	10.203%	$62.6394	$62.64	$62.65	$62.60
Purchase #3	$102.54	4.334%	$106.9841	$106.98	$107.00	$107.00
Purchase #4	$232.63	12.764%	$262.3229	$262.32	$262.30	$262.30
Purchase #5	$130.57	6.666%	$139.2738	$139.27	$139.25	$139.30
Purchase #6	$118.52	11.128%	$131.7089	$131.71	$131.70	$131.70
Purchase #7	$165.98	8.394%	$179.9124	$179.91	$179.90	$179.90
7 purchase totals =	$836.84		$914.4413	$914.43	$914.40	$914.40