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	$117.28	11.760%	$131.0721	$131.07	$131.05	$131.10
Purchase #2	$179.82	6.414%	$191.3537	$191.35	$191.35	$191.40
Purchase #3	$39.80	12.647%	$44.8335	$44.83	$44.85	$44.80
Purchase #4	$248.66	11.785%	$277.9646	$277.96	$277.95	$278.00
Purchase #5	$249.43	5.446%	$263.014	$263.01	$263.00	$263.00
Purchase #6	$102.86	10.335%	$113.4906	$113.49	$113.50	$113.50
Purchase #7	$100.57	8.813%	$109.4332	$109.43	$109.45	$109.40
7 purchase totals =	$1,038.42		$1,131.1617	$1,131.14	$1,131.15	$1,131.20