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	$143.59	3.605%	$148.7664	$148.77	$148.75	$148.80
Purchase #2	$52.34	7.687%	$56.3634	$56.36	$56.35	$56.40
Purchase #3	$203.27	3.264%	$209.9047	$209.90	$209.90	$209.90
Purchase #4	$146.86	12.645%	$165.4304	$165.43	$165.45	$165.40
Purchase #5	$202.62	10.451%	$223.7958	$223.80	$223.80	$223.80
Purchase #6	$40.97	10.220%	$45.1571	$45.16	$45.15	$45.20
Purchase #7	$175.82	12.447%	$197.7043	$197.70	$197.70	$197.70
7 purchase totals =	$965.47		$1,047.1221	$1,047.12	$1,047.10	$1,047.20