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	$57.49	6.326%	$61.1268	$61.13	$61.15	$61.10
Purchase #2	$52.75	8.608%	$57.2907	$57.29	$57.30	$57.30
Purchase #3	$80.29	3.740%	$83.2928	$83.29	$83.30	$83.30
Purchase #4	$231.47	12.780%	$261.0519	$261.05	$261.05	$261.10
Purchase #5	$42.64	8.704%	$46.3514	$46.35	$46.35	$46.40
Purchase #6	$51.30	7.434%	$55.1136	$55.11	$55.10	$55.10
Purchase #7	$97.43	3.840%	$101.1713	$101.17	$101.15	$101.20
7 purchase totals =	$613.37		$665.3985	$665.39	$665.40	$665.50