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	$209.70	11.369%	$233.5408	$233.54	$233.55	$233.50
Purchase #2	$49.70	4.393%	$51.8833	$51.88	$51.90	$51.90
Purchase #3	$116.41	12.537%	$131.0043	$131.00	$131.00	$131.00
Purchase #4	$102.84	3.527%	$106.4672	$106.47	$106.45	$106.50
Purchase #5	$74.29	4.735%	$77.8076	$77.81	$77.80	$77.80
Purchase #6	$80.51	6.234%	$85.529	$85.53	$85.55	$85.50
Purchase #7	$158.76	4.723%	$166.2582	$166.26	$166.25	$166.30
7 purchase totals =	$792.21		$852.4904	$852.49	$852.50	$852.50