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	$68.42	3.714%	$70.9611	$70.96	$70.95	$71.00
Purchase #2	$40.49	4.673%	$42.3821	$42.38	$42.40	$42.40
Purchase #3	$81.31	10.367%	$89.7394	$89.74	$89.75	$89.70
Purchase #4	$157.71	12.520%	$177.4553	$177.46	$177.45	$177.50
Purchase #5	$75.52	3.729%	$78.3361	$78.34	$78.35	$78.30
Purchase #6	$187.38	6.374%	$199.3236	$199.32	$199.30	$199.30
Purchase #7	$167.34	4.619%	$175.0694	$175.07	$175.05	$175.10
7 purchase totals =	$778.17		$833.2670	$833.27	$833.25	$833.30