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	$102.99	6.300%	$109.4784	$109.48	$109.50	$109.50
Purchase #2	$239.94	9.596%	$262.9646	$262.96	$262.95	$263.00
Purchase #3	$79.31	4.393%	$82.7941	$82.79	$82.80	$82.80
Purchase #4	$234.98	8.568%	$255.1131	$255.11	$255.10	$255.10
Purchase #5	$114.78	12.454%	$129.0747	$129.07	$129.05	$129.10
Purchase #6	$89.83	10.245%	$99.0331	$99.03	$99.05	$99.00
Purchase #7	$221.46	9.116%	$241.6483	$241.65	$241.65	$241.60
7 purchase totals =	$1,083.29		$1,180.1063	$1,180.09	$1,180.10	$1,180.10