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	$62.43	8.591%	$67.7934	$67.79	$67.80	$67.80
Purchase #2	$85.34	13.298%	$96.6885	$96.69	$96.70	$96.70
Purchase #3	$153.39	11.163%	$170.5129	$170.51	$170.50	$170.50
Purchase #4	$112.28	3.795%	$116.541	$116.54	$116.55	$116.50
Purchase #5	$110.76	8.633%	$120.3219	$120.32	$120.30	$120.30
Purchase #6	$151.51	11.390%	$168.767	$168.77	$168.75	$168.80
Purchase #7	$31.64	4.340%	$33.0132	$33.01	$33.00	$33.00
7 purchase totals =	$707.35		$773.6379	$773.63	$773.60	$773.60