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	$98.50	6.494%	$104.8966	$104.90	$104.90	$104.90
Purchase #2	$102.29	13.102%	$115.692	$115.69	$115.70	$115.70
Purchase #3	$222.79	7.223%	$238.8821	$238.88	$238.90	$238.90
Purchase #4	$94.80	12.295%	$106.4557	$106.46	$106.45	$106.50
Purchase #5	$82.69	13.683%	$94.0045	$94.00	$94.00	$94.00
Purchase #6	$87.45	13.661%	$99.3965	$99.40	$99.40	$99.40
Purchase #7	$114.77	8.496%	$124.5209	$124.52	$124.50	$124.50
7 purchase totals =	$803.29		$883.8483	$883.85	$883.85	$883.90