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	$37.28	12.809%	$42.0552	$42.06	$42.05	$42.10
Purchase #2	$88.86	13.492%	$100.849	$100.85	$100.85	$100.80
Purchase #3	$119.86	7.361%	$128.6829	$128.68	$128.70	$128.70
Purchase #4	$22.64	10.679%	$25.0577	$25.06	$25.05	$25.10
Purchase #5	$184.81	8.680%	$200.8515	$200.85	$200.85	$200.90
Purchase #6	$28.86	11.391%	$32.1474	$32.15	$32.15	$32.10
Purchase #7	$166.74	9.688%	$182.8938	$182.89	$182.90	$182.90
7 purchase totals =	$649.05		$712.5375	$712.54	$712.55	$712.60