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	$117.85	5.502%	$124.3341	$124.33	$124.35	$124.30
Purchase #2	$237.78	7.854%	$256.4552	$256.46	$256.45	$256.50
Purchase #3	$86.64	13.471%	$98.3113	$98.31	$98.30	$98.30
Purchase #4	$37.26	7.716%	$40.135	$40.14	$40.15	$40.10
Purchase #5	$63.71	5.349%	$67.1178	$67.12	$67.10	$67.10
Purchase #6	$93.85	5.603%	$99.1084	$99.11	$99.10	$99.10
Purchase #7	$101.85	13.363%	$115.4602	$115.46	$115.45	$115.50
7 purchase totals =	$738.94		$800.9220	$800.93	$800.90	$800.90