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	$135.38	13.394%	$153.5128	$153.51	$153.50	$153.50
Purchase #2	$203.56	9.585%	$223.0712	$223.07	$223.05	$223.10
Purchase #3	$166.67	7.682%	$179.4736	$179.47	$179.45	$179.50
Purchase #4	$216.88	13.339%	$245.8096	$245.81	$245.80	$245.80
Purchase #5	$73.61	6.683%	$78.5294	$78.53	$78.55	$78.50
Purchase #6	$103.70	11.443%	$115.5664	$115.57	$115.55	$115.60
Purchase #7	$83.87	5.486%	$88.4711	$88.47	$88.45	$88.50
7 purchase totals =	$983.67		$1,084.4341	$1,084.43	$1,084.35	$1,084.50