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	$131.28	8.256%	$142.1185	$142.12	$142.10	$142.10
Purchase #2	$243.87	3.219%	$251.7202	$251.72	$251.70	$251.70
Purchase #3	$38.39	10.441%	$42.3983	$42.40	$42.40	$42.40
Purchase #4	$219.96	9.825%	$241.5711	$241.57	$241.55	$241.60
Purchase #5	$232.53	3.840%	$241.4592	$241.46	$241.45	$241.50
Purchase #6	$229.52	7.682%	$247.1517	$247.15	$247.15	$247.20
Purchase #7	$131.59	8.763%	$143.1212	$143.12	$143.10	$143.10
7 purchase totals =	$1,227.14		$1,309.5402	$1,309.54	$1,309.45	$1,309.60