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	$246.49	7.268%	$264.4049	$264.40	$264.40	$264.40
Purchase #2	$106.34	11.405%	$118.4681	$118.47	$118.45	$118.50
Purchase #3	$194.77	5.387%	$205.2623	$205.26	$205.25	$205.30
Purchase #4	$161.80	7.824%	$174.4592	$174.46	$174.45	$174.50
Purchase #5	$85.76	6.217%	$91.0917	$91.09	$91.10	$91.10
Purchase #6	$25.86	9.646%	$28.3545	$28.35	$28.35	$28.40
Purchase #7	$87.54	13.661%	$99.4988	$99.50	$99.50	$99.50
7 purchase totals =	$908.56		$981.5395	$981.53	$981.50	$981.70