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	$137.55	9.391%	$150.4673	$150.47	$150.45	$150.50
Purchase #2	$161.38	11.358%	$179.7095	$179.71	$179.70	$179.70
Purchase #3	$164.39	13.344%	$186.3262	$186.33	$186.35	$186.30
Purchase #4	$18.45	12.252%	$20.7105	$20.71	$20.70	$20.70
Purchase #5	$177.40	8.204%	$191.9539	$191.95	$191.95	$192.00
Purchase #6	$180.41	4.676%	$188.846	$188.85	$188.85	$188.80
Purchase #7	$90.43	10.266%	$99.7135	$99.71	$99.70	$99.70
7 purchase totals =	$930.01		$1,017.7269	$1,017.73	$1,017.70	$1,017.70