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	$232.79	9.756%	$255.501	$255.50	$255.50	$255.50
Purchase #2	$117.62	9.476%	$128.7657	$128.77	$128.75	$128.80
Purchase #3	$131.55	12.314%	$147.7491	$147.75	$147.75	$147.70
Purchase #4	$166.66	3.261%	$172.0948	$172.09	$172.10	$172.10
Purchase #5	$178.90	7.505%	$192.3264	$192.33	$192.35	$192.30
Purchase #6	$159.73	5.385%	$168.3315	$168.33	$168.35	$168.30
Purchase #7	$242.65	7.719%	$261.3802	$261.38	$261.40	$261.40
7 purchase totals =	$1,229.90		$1,326.1487	$1,326.15	$1,326.20	$1,326.10