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	$250.99	11.672%	$280.2856	$280.29	$280.30	$280.30
Purchase #2	$198.56	11.507%	$221.4083	$221.41	$221.40	$221.40
Purchase #3	$197.63	10.739%	$218.8535	$218.85	$218.85	$218.90
Purchase #4	$188.87	5.148%	$198.593	$198.59	$198.60	$198.60
Purchase #5	$20.76	10.195%	$22.8765	$22.88	$22.90	$22.90
Purchase #6	$102.89	13.272%	$116.5456	$116.55	$116.55	$116.50
Purchase #7	$16.69	11.612%	$18.628	$18.63	$18.65	$18.60
7 purchase totals =	$976.39		$1,077.1905	$1,077.20	$1,077.25	$1,077.20