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	$93.51	7.451%	$100.4774	$100.48	$100.50	$100.50
Purchase #2	$55.27	6.773%	$59.0134	$59.01	$59.00	$59.00
Purchase #3	$103.61	11.729%	$115.7624	$115.76	$115.75	$115.80
Purchase #4	$57.46	4.402%	$59.9894	$59.99	$60.00	$60.00
Purchase #5	$63.76	13.350%	$72.272	$72.27	$72.25	$72.30
Purchase #6	$234.85	13.614%	$266.8225	$266.82	$266.80	$266.80
Purchase #7	$6.80	12.145%	$7.6259	$7.63	$7.65	$7.60
7 purchase totals =	$615.26		$681.9630	$681.96	$681.95	$682.00