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	$136.75	12.828%	$154.2923	$154.29	$154.30	$154.30
Purchase #2	$161.34	8.781%	$175.5073	$175.51	$175.50	$175.50
Purchase #3	$202.46	6.482%	$215.5835	$215.58	$215.60	$215.60
Purchase #4	$144.83	7.314%	$155.4229	$155.42	$155.40	$155.40
Purchase #5	$228.98	7.376%	$245.8696	$245.87	$245.85	$245.90
Purchase #6	$27.84	13.494%	$31.5967	$31.60	$31.60	$31.60
Purchase #7	$85.80	4.478%	$89.6421	$89.64	$89.65	$89.60
7 purchase totals =	$988.00		$1,067.9144	$1,067.91	$1,067.90	$1,067.90