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	$29.84	12.697%	$33.6288	$33.63	$33.65	$33.60
Purchase #2	$87.54	4.767%	$91.713	$91.71	$91.70	$91.70
Purchase #3	$119.67	10.396%	$132.1109	$132.11	$132.10	$132.10
Purchase #4	$121.47	13.528%	$137.9025	$137.90	$137.90	$137.90
Purchase #5	$28.67	12.623%	$32.289	$32.29	$32.30	$32.30
Purchase #6	$18.35	13.426%	$20.8137	$20.81	$20.80	$20.80
Purchase #7	$212.39	13.415%	$240.8821	$240.88	$240.90	$240.90
7 purchase totals =	$617.93		$689.3400	$689.33	$689.35	$689.30