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	$108.51	13.848%	$123.5365	$123.54	$123.55	$123.50
Purchase #2	$98.98	6.835%	$105.7453	$105.75	$105.75	$105.70
Purchase #3	$228.56	4.471%	$238.7789	$238.78	$238.80	$238.80
Purchase #4	$89.53	4.869%	$93.8892	$93.89	$93.90	$93.90
Purchase #5	$53.69	6.846%	$57.3656	$57.37	$57.35	$57.40
Purchase #6	$119.43	13.229%	$135.2294	$135.23	$135.25	$135.20
Purchase #7	$235.55	5.511%	$248.5312	$248.53	$248.55	$248.50
7 purchase totals =	$934.25		$1,003.0761	$1,003.09	$1,003.15	$1,003.00