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	$215.69	7.350%	$231.5432	$231.54	$231.55	$231.50
Purchase #2	$142.86	5.596%	$150.8544	$150.85	$150.85	$150.90
Purchase #3	$23.68	11.547%	$26.4143	$26.41	$26.40	$26.40
Purchase #4	$241.70	6.740%	$257.9906	$257.99	$258.00	$258.00
Purchase #5	$98.71	5.258%	$103.9002	$103.90	$103.90	$103.90
Purchase #6	$28.79	10.533%	$31.8225	$31.82	$31.80	$31.80
Purchase #7	$190.59	13.556%	$216.4264	$216.43	$216.45	$216.40
7 purchase totals =	$942.02		$1,018.9516	$1,018.94	$1,018.95	$1,018.90