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	$38.43	9.469%	$42.0689	$42.07	$42.05	$42.10
Purchase #2	$8.93	13.109%	$10.1006	$10.10	$10.10	$10.10
Purchase #3	$103.78	13.441%	$117.7291	$117.73	$117.75	$117.70
Purchase #4	$184.96	3.320%	$191.1007	$191.10	$191.10	$191.10
Purchase #5	$75.69	3.565%	$78.3883	$78.39	$78.40	$78.40
Purchase #6	$211.98	12.160%	$237.7568	$237.76	$237.75	$237.80
Purchase #7	$23.39	9.154%	$25.5311	$25.53	$25.55	$25.50
7 purchase totals =	$647.16		$702.6755	$702.68	$702.70	$702.70