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	$191.73	13.848%	$218.2808	$218.28	$218.30	$218.30
Purchase #2	$170.75	11.600%	$190.557	$190.56	$190.55	$190.60
Purchase #3	$7.50	5.247%	$7.8935	$7.89	$7.90	$7.90
Purchase #4	$167.61	12.595%	$188.7205	$188.72	$188.70	$188.70
Purchase #5	$7.72	3.301%	$7.9748	$7.97	$7.95	$8.00
Purchase #6	$232.88	7.543%	$250.4461	$250.45	$250.45	$250.40
Purchase #7	$241.90	7.351%	$259.6821	$259.68	$259.70	$259.70
7 purchase totals =	$1,020.09		$1,123.5548	$1,123.55	$1,123.55	$1,123.60