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	$196.46	13.171%	$222.3357	$222.34	$222.35	$222.30
Purchase #2	$16.56	13.111%	$18.7312	$18.73	$18.75	$18.70
Purchase #3	$223.85	12.166%	$251.0836	$251.08	$251.10	$251.10
Purchase #4	$69.61	3.249%	$71.8716	$71.87	$71.85	$71.90
Purchase #5	$183.47	5.430%	$193.4324	$193.43	$193.45	$193.40
Purchase #6	$56.45	3.315%	$58.3213	$58.32	$58.30	$58.30
Purchase #7	$242.46	9.215%	$264.8027	$264.80	$264.80	$264.80
7 purchase totals =	$988.86		$1,080.5785	$1,080.57	$1,080.60	$1,080.50