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	$20.53	6.471%	$21.8585	$21.86	$21.85	$21.90
Purchase #2	$161.55	13.246%	$182.9489	$182.95	$182.95	$182.90
Purchase #3	$47.37	8.700%	$51.4912	$51.49	$51.50	$51.50
Purchase #4	$11.93	13.322%	$13.5193	$13.52	$13.50	$13.50
Purchase #5	$79.63	10.772%	$88.2077	$88.21	$88.20	$88.20
Purchase #6	$188.37	4.331%	$196.5283	$196.53	$196.55	$196.50
Purchase #7	$110.71	4.104%	$115.2535	$115.25	$115.25	$115.30
7 purchase totals =	$620.09		$669.8074	$669.81	$669.80	$669.80