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	$67.88	5.740%	$71.7763	$71.78	$71.80	$71.80
Purchase #2	$248.30	8.825%	$270.2125	$270.21	$270.20	$270.20
Purchase #3	$168.34	10.345%	$185.7548	$185.75	$185.75	$185.80
Purchase #4	$112.65	4.725%	$117.9727	$117.97	$117.95	$118.00
Purchase #5	$195.27	10.558%	$215.8866	$215.89	$215.90	$215.90
Purchase #6	$121.64	5.324%	$128.1161	$128.12	$128.10	$128.10
Purchase #7	$66.32	7.265%	$71.1381	$71.14	$71.15	$71.10
7 purchase totals =	$980.40		$1,060.8571	$1,060.86	$1,060.85	$1,060.90