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	$140.89	9.110%	$153.7251	$153.73	$153.75	$153.70
Purchase #2	$65.96	10.226%	$72.7051	$72.71	$72.70	$72.70
Purchase #3	$152.78	12.132%	$171.3153	$171.32	$171.30	$171.30
Purchase #4	$13.63	3.300%	$14.0798	$14.08	$14.10	$14.10
Purchase #5	$92.96	4.708%	$97.3366	$97.34	$97.35	$97.30
Purchase #6	$39.56	6.772%	$42.239	$42.24	$42.25	$42.20
Purchase #7	$81.92	11.393%	$91.2531	$91.25	$91.25	$91.30
7 purchase totals =	$587.70		$642.6540	$642.67	$642.70	$642.60