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	$237.96	13.851%	$270.9198	$270.92	$270.90	$270.90
Purchase #2	$130.27	6.797%	$139.1245	$139.12	$139.10	$139.10
Purchase #3	$212.87	10.512%	$235.2469	$235.25	$235.25	$235.20
Purchase #4	$134.48	3.667%	$139.4114	$139.41	$139.40	$139.40
Purchase #5	$222.95	6.291%	$236.9758	$236.98	$237.00	$237.00
Purchase #6	$83.83	3.855%	$87.0616	$87.06	$87.05	$87.10
Purchase #7	$83.33	7.818%	$89.8447	$89.84	$89.85	$89.80
7 purchase totals =	$1,105.69		$1,198.5847	$1,198.58	$1,198.55	$1,198.50