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	$119.73	3.410%	$123.8128	$123.81	$123.80	$123.80
Purchase #2	$236.40	10.629%	$261.527	$261.53	$261.55	$261.50
Purchase #3	$176.44	10.309%	$194.6292	$194.63	$194.65	$194.60
Purchase #4	$67.77	5.406%	$71.4336	$71.43	$71.45	$71.40
Purchase #5	$157.92	13.505%	$179.2471	$179.25	$179.25	$179.20
Purchase #6	$248.90	13.557%	$282.6434	$282.64	$282.65	$282.60
Purchase #7	$160.38	4.300%	$167.2763	$167.28	$167.30	$167.30
7 purchase totals =	$1,167.54		$1,280.5694	$1,280.57	$1,280.65	$1,280.40