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	$136.57	4.369%	$142.5367	$142.54	$142.55	$142.50
Purchase #2	$137.99	3.736%	$143.1453	$143.15	$143.15	$143.10
Purchase #3	$109.62	12.469%	$123.2885	$123.29	$123.30	$123.30
Purchase #4	$21.95	12.617%	$24.7194	$24.72	$24.70	$24.70
Purchase #5	$101.87	4.559%	$106.5143	$106.51	$106.50	$106.50
Purchase #6	$43.62	4.769%	$45.7002	$45.70	$45.70	$45.70
Purchase #7	$236.76	3.240%	$244.431	$244.43	$244.45	$244.40
7 purchase totals =	$788.38		$830.3354	$830.34	$830.35	$830.20