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	$14.57	12.498%	$16.391	$16.39	$16.40	$16.40
Purchase #2	$116.31	13.434%	$131.9351	$131.94	$131.95	$131.90
Purchase #3	$31.36	11.319%	$34.9096	$34.91	$34.90	$34.90
Purchase #4	$18.72	5.700%	$19.787	$19.79	$19.80	$19.80
Purchase #5	$152.89	3.372%	$158.0455	$158.05	$158.05	$158.00
Purchase #6	$90.93	3.726%	$94.3181	$94.32	$94.30	$94.30
Purchase #7	$187.46	9.297%	$204.8882	$204.89	$204.90	$204.90
7 purchase totals =	$612.24		$660.2745	$660.29	$660.30	$660.20