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	$57.46	3.449%	$59.4418	$59.44	$59.45	$59.40
Purchase #2	$24.61	12.510%	$27.6887	$27.69	$27.70	$27.70
Purchase #3	$28.28	4.708%	$29.6114	$29.61	$29.60	$29.60
Purchase #4	$232.86	7.662%	$250.7017	$250.70	$250.70	$250.70
Purchase #5	$164.49	4.251%	$171.4825	$171.48	$171.50	$171.50
Purchase #6	$165.33	10.472%	$182.6434	$182.64	$182.65	$182.60
Purchase #7	$154.40	9.524%	$169.1051	$169.11	$169.10	$169.10
7 purchase totals =	$827.43		$890.6746	$890.67	$890.70	$890.60