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	$225.98	6.428%	$240.506	$240.51	$240.50	$240.50
Purchase #2	$116.46	7.215%	$124.8626	$124.86	$124.85	$124.90
Purchase #3	$52.88	3.873%	$54.928	$54.93	$54.95	$54.90
Purchase #4	$77.41	7.154%	$82.9479	$82.95	$82.95	$82.90
Purchase #5	$43.63	5.250%	$45.9206	$45.92	$45.90	$45.90
Purchase #6	$7.44	10.116%	$8.1926	$8.19	$8.20	$8.20
Purchase #7	$241.87	12.170%	$271.3056	$271.31	$271.30	$271.30
7 purchase totals =	$765.67		$828.6633	$828.67	$828.65	$828.60