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	$174.96	8.507%	$189.8438	$189.84	$189.85	$189.80
Purchase #2	$37.82	12.312%	$42.4764	$42.48	$42.50	$42.50
Purchase #3	$19.25	6.160%	$20.4358	$20.44	$20.45	$20.40
Purchase #4	$192.28	13.866%	$218.9415	$218.94	$218.95	$218.90
Purchase #5	$161.67	13.168%	$182.9587	$182.96	$182.95	$183.00
Purchase #6	$243.72	5.152%	$256.2765	$256.28	$256.30	$256.30
Purchase #7	$18.78	9.175%	$20.5031	$20.50	$20.50	$20.50
7 purchase totals =	$848.48		$931.4358	$931.44	$931.50	$931.40