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	$19.83	5.724%	$20.9651	$20.97	$20.95	$21.00
Purchase #2	$32.80	8.260%	$35.5093	$35.51	$35.50	$35.50
Purchase #3	$131.34	6.332%	$139.6564	$139.66	$139.65	$139.70
Purchase #4	$172.90	10.540%	$191.1237	$191.12	$191.10	$191.10
Purchase #5	$79.83	7.402%	$85.739	$85.74	$85.75	$85.70
Purchase #6	$127.92	5.826%	$135.3726	$135.37	$135.35	$135.40
Purchase #7	$83.65	5.834%	$88.5301	$88.53	$88.55	$88.50
7 purchase totals =	$648.27		$696.8962	$696.90	$696.85	$696.90