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	$246.66	12.789%	$278.2053	$278.21	$278.20	$278.20
Purchase #2	$162.72	9.109%	$177.5422	$177.54	$177.55	$177.50
Purchase #3	$238.96	10.229%	$263.4032	$263.40	$263.40	$263.40
Purchase #4	$71.44	9.595%	$78.2947	$78.29	$78.30	$78.30
Purchase #5	$247.53	12.248%	$277.8475	$277.85	$277.85	$277.80
Purchase #6	$246.56	3.822%	$255.9835	$255.98	$256.00	$256.00
Purchase #7	$154.68	6.857%	$165.2864	$165.29	$165.30	$165.30
7 purchase totals =	$1,368.55		$1,496.5628	$1,496.56	$1,496.60	$1,496.50