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	$131.64	12.298%	$147.8291	$147.83	$147.85	$147.80
Purchase #2	$97.63	8.492%	$105.9207	$105.92	$105.90	$105.90
Purchase #3	$147.91	7.234%	$158.6098	$158.61	$158.60	$158.60
Purchase #4	$171.32	13.441%	$194.3471	$194.35	$194.35	$194.30
Purchase #5	$179.80	8.786%	$195.5972	$195.60	$195.60	$195.60
Purchase #6	$39.25	11.627%	$43.8136	$43.81	$43.80	$43.80
Purchase #7	$79.93	13.825%	$90.9803	$90.98	$91.00	$91.00
7 purchase totals =	$847.48		$937.0978	$937.10	$937.10	$937.00