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	$6.85	6.677%	$7.3074	$7.31	$7.30	$7.30
Purchase #2	$196.46	7.473%	$211.1415	$211.14	$211.15	$211.10
Purchase #3	$166.87	9.420%	$182.5892	$182.59	$182.60	$182.60
Purchase #4	$189.56	7.118%	$203.0529	$203.05	$203.05	$203.10
Purchase #5	$140.89	13.186%	$159.4678	$159.47	$159.45	$159.50
Purchase #6	$29.93	5.563%	$31.595	$31.60	$31.60	$31.60
Purchase #7	$93.27	11.405%	$103.9074	$103.91	$103.90	$103.90
7 purchase totals =	$823.83		$899.0612	$899.07	$899.05	$899.10