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	$27.69	12.785%	$31.2302	$31.23	$31.25	$31.20
Purchase #2	$178.35	5.351%	$187.8935	$187.89	$187.90	$187.90
Purchase #3	$144.53	10.490%	$159.6912	$159.69	$159.70	$159.70
Purchase #4	$19.75	10.835%	$21.8899	$21.89	$21.90	$21.90
Purchase #5	$185.88	3.157%	$191.7482	$191.75	$191.75	$191.70
Purchase #6	$160.79	7.404%	$172.6949	$172.69	$172.70	$172.70
Purchase #7	$218.97	11.556%	$244.2742	$244.27	$244.25	$244.30
7 purchase totals =	$935.96		$1,009.4221	$1,009.41	$1,009.45	$1,009.40