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	$126.86	6.495%	$135.0996	$135.10	$135.10	$135.10
Purchase #2	$151.30	6.104%	$160.5354	$160.54	$160.55	$160.50
Purchase #3	$93.65	13.604%	$106.3901	$106.39	$106.40	$106.40
Purchase #4	$41.73	4.112%	$43.4459	$43.45	$43.45	$43.40
Purchase #5	$117.34	11.488%	$130.82	$130.82	$130.80	$130.80
Purchase #6	$245.80	3.783%	$255.0986	$255.10	$255.10	$255.10
Purchase #7	$143.83	4.395%	$150.1513	$150.15	$150.15	$150.20
7 purchase totals =	$920.51		$981.5409	$981.55	$981.55	$981.50