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	$136.79	12.610%	$154.0392	$154.04	$154.05	$154.00
Purchase #2	$236.95	9.111%	$258.5385	$258.54	$258.55	$258.50
Purchase #3	$184.45	3.759%	$191.3835	$191.38	$191.40	$191.40
Purchase #4	$73.33	6.623%	$78.1866	$78.19	$78.20	$78.20
Purchase #5	$51.85	9.254%	$56.6482	$56.65	$56.65	$56.60
Purchase #6	$43.30	5.112%	$45.5135	$45.51	$45.50	$45.50
Purchase #7	$14.34	3.372%	$14.8235	$14.82	$14.80	$14.80
7 purchase totals =	$741.01		$799.1330	$799.13	$799.15	$799.00