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	$112.80	7.392%	$121.1382	$121.14	$121.15	$121.10
Purchase #2	$198.55	10.176%	$218.7544	$218.75	$218.75	$218.80
Purchase #3	$94.71	4.760%	$99.2182	$99.22	$99.20	$99.20
Purchase #4	$135.28	5.199%	$142.3132	$142.31	$142.30	$142.30
Purchase #5	$51.96	6.789%	$55.4876	$55.49	$55.50	$55.50
Purchase #6	$217.92	9.332%	$238.2563	$238.26	$238.25	$238.30
Purchase #7	$31.53	3.787%	$32.724	$32.72	$32.70	$32.70
7 purchase totals =	$842.75		$907.8919	$907.89	$907.85	$907.90