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	$173.75	3.830%	$180.4046	$180.40	$180.40	$180.40
Purchase #2	$232.94	13.232%	$263.7626	$263.76	$263.75	$263.80
Purchase #3	$101.40	8.324%	$109.8405	$109.84	$109.85	$109.80
Purchase #4	$146.49	12.838%	$165.2964	$165.30	$165.30	$165.30
Purchase #5	$124.97	5.646%	$132.0258	$132.03	$132.05	$132.00
Purchase #6	$59.27	9.485%	$64.8918	$64.89	$64.90	$64.90
Purchase #7	$109.30	12.850%	$123.3451	$123.35	$123.35	$123.30
7 purchase totals =	$948.12		$1,039.5668	$1,039.57	$1,039.60	$1,039.50