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	$68.27	12.753%	$76.9765	$76.98	$77.00	$77.00
Purchase #2	$52.55	12.355%	$59.0426	$59.04	$59.05	$59.00
Purchase #3	$101.86	10.315%	$112.3669	$112.37	$112.35	$112.40
Purchase #4	$150.27	3.376%	$155.3431	$155.34	$155.35	$155.30
Purchase #5	$139.28	11.761%	$155.6607	$155.66	$155.65	$155.70
Purchase #6	$250.58	5.593%	$264.5949	$264.59	$264.60	$264.60
Purchase #7	$225.86	13.739%	$256.8909	$256.89	$256.90	$256.90
7 purchase totals =	$988.67		$1,080.8756	$1,080.87	$1,080.90	$1,080.90