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	$240.47	3.327%	$248.4704	$248.47	$248.45	$248.50
Purchase #2	$101.82	9.689%	$111.6853	$111.69	$111.70	$111.70
Purchase #3	$41.85	5.399%	$44.1095	$44.11	$44.10	$44.10
Purchase #4	$111.60	6.647%	$119.0181	$119.02	$119.00	$119.00
Purchase #5	$228.52	12.376%	$256.8016	$256.80	$256.80	$256.80
Purchase #6	$240.89	10.557%	$266.3208	$266.32	$266.30	$266.30
Purchase #7	$75.43	12.851%	$85.1235	$85.12	$85.10	$85.10
7 purchase totals =	$1,040.58		$1,131.5292	$1,131.53	$1,131.45	$1,131.50