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	$250.27	12.197%	$280.7954	$280.80	$280.80	$280.80
Purchase #2	$84.53	12.295%	$94.923	$94.92	$94.90	$94.90
Purchase #3	$235.57	8.504%	$255.6029	$255.60	$255.60	$255.60
Purchase #4	$77.87	4.410%	$81.3041	$81.30	$81.30	$81.30
Purchase #5	$27.96	6.549%	$29.7911	$29.79	$29.80	$29.80
Purchase #6	$68.87	4.146%	$71.7254	$71.73	$71.75	$71.70
Purchase #7	$90.66	10.745%	$100.4014	$100.40	$100.40	$100.40
7 purchase totals =	$835.73		$914.5433	$914.54	$914.55	$914.50