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	$27.43	11.210%	$30.5049	$30.50	$30.50	$30.50
Purchase #2	$83.27	12.211%	$93.4381	$93.44	$93.45	$93.40
Purchase #3	$30.27	4.489%	$31.6288	$31.63	$31.65	$31.60
Purchase #4	$125.39	13.745%	$142.6249	$142.62	$142.60	$142.60
Purchase #5	$119.91	9.385%	$131.1636	$131.16	$131.15	$131.20
Purchase #6	$108.91	4.798%	$114.1355	$114.14	$114.15	$114.10
Purchase #7	$119.67	10.232%	$131.9146	$131.91	$131.90	$131.90
7 purchase totals =	$614.85		$675.4104	$675.40	$675.40	$675.30