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	$168.89	6.301%	$179.5318	$179.53	$179.55	$179.50
Purchase #2	$77.36	11.668%	$86.3864	$86.39	$86.40	$86.40
Purchase #3	$194.84	6.196%	$206.9123	$206.91	$206.90	$206.90
Purchase #4	$69.79	5.252%	$73.4554	$73.46	$73.45	$73.50
Purchase #5	$221.29	13.186%	$250.4693	$250.47	$250.45	$250.50
Purchase #6	$73.62	8.734%	$80.05	$80.05	$80.05	$80.10
Purchase #7	$182.66	7.531%	$196.4161	$196.42	$196.40	$196.40
7 purchase totals =	$988.45		$1,073.2213	$1,073.23	$1,073.20	$1,073.30