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	$145.50	3.769%	$150.9839	$150.98	$151.00	$151.00
Purchase #2	$210.80	13.435%	$239.121	$239.12	$239.10	$239.10
Purchase #3	$231.73	13.515%	$263.0483	$263.05	$263.05	$263.00
Purchase #4	$7.56	11.792%	$8.4515	$8.45	$8.45	$8.50
Purchase #5	$178.66	6.316%	$189.9442	$189.94	$189.95	$189.90
Purchase #6	$18.63	13.227%	$21.0942	$21.09	$21.10	$21.10
Purchase #7	$89.69	12.490%	$100.8923	$100.89	$100.90	$100.90
7 purchase totals =	$882.57		$973.5354	$973.52	$973.55	$973.50