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	$217.78	6.188%	$231.2562	$231.26	$231.25	$231.30
Purchase #2	$246.43	13.782%	$280.393	$280.39	$280.40	$280.40
Purchase #3	$47.59	11.192%	$52.9163	$52.92	$52.90	$52.90
Purchase #4	$127.76	12.738%	$144.0341	$144.03	$144.05	$144.00
Purchase #5	$133.61	13.610%	$151.7943	$151.79	$151.80	$151.80
Purchase #6	$81.82	5.571%	$86.3782	$86.38	$86.40	$86.40
Purchase #7	$96.74	13.128%	$109.44	$109.44	$109.45	$109.40
7 purchase totals =	$951.73		$1,056.2121	$1,056.21	$1,056.25	$1,056.20