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	$131.78	10.576%	$145.7171	$145.72	$145.70	$145.70
Purchase #2	$222.40	4.416%	$232.2212	$232.22	$232.20	$232.20
Purchase #3	$124.91	13.686%	$142.0052	$142.01	$142.00	$142.00
Purchase #4	$57.36	4.310%	$59.8322	$59.83	$59.85	$59.80
Purchase #5	$11.78	13.102%	$13.3234	$13.32	$13.30	$13.30
Purchase #6	$151.32	4.420%	$158.0083	$158.01	$158.00	$158.00
Purchase #7	$228.79	9.557%	$250.6555	$250.66	$250.65	$250.70
7 purchase totals =	$928.34		$1,001.7629	$1,001.77	$1,001.70	$1,001.70