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	$77.27	6.563%	$82.3412	$82.34	$82.35	$82.30
Purchase #2	$115.60	12.263%	$129.776	$129.78	$129.80	$129.80
Purchase #3	$248.95	12.564%	$280.2281	$280.23	$280.25	$280.20
Purchase #4	$235.71	8.568%	$255.9056	$255.91	$255.90	$255.90
Purchase #5	$53.54	11.273%	$59.5756	$59.58	$59.60	$59.60
Purchase #6	$129.52	10.862%	$143.5885	$143.59	$143.60	$143.60
Purchase #7	$165.98	7.333%	$178.1513	$178.15	$178.15	$178.20
7 purchase totals =	$1,026.57		$1,129.5663	$1,129.58	$1,129.65	$1,129.60