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	$19.77	13.551%	$22.449	$22.45	$22.45	$22.40
Purchase #2	$99.96	6.173%	$106.1305	$106.13	$106.15	$106.10
Purchase #3	$127.37	12.132%	$142.8225	$142.82	$142.80	$142.80
Purchase #4	$61.36	9.598%	$67.2493	$67.25	$67.25	$67.20
Purchase #5	$234.45	9.157%	$255.9186	$255.92	$255.90	$255.90
Purchase #6	$176.78	12.488%	$198.8563	$198.86	$198.85	$198.90
Purchase #7	$116.79	6.541%	$124.4292	$124.43	$124.45	$124.40
7 purchase totals =	$836.48		$917.8554	$917.86	$917.85	$917.70