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	$225.26	12.372%	$253.1292	$253.13	$253.15	$253.10
Purchase #2	$41.71	9.232%	$45.5607	$45.56	$45.55	$45.60
Purchase #3	$38.92	7.525%	$41.8487	$41.85	$41.85	$41.80
Purchase #4	$98.62	3.356%	$101.9297	$101.93	$101.95	$101.90
Purchase #5	$93.89	4.795%	$98.392	$98.39	$98.40	$98.40
Purchase #6	$61.54	9.290%	$67.2571	$67.26	$67.25	$67.30
Purchase #7	$19.45	6.722%	$20.7574	$20.76	$20.75	$20.80
7 purchase totals =	$579.39		$628.8748	$628.88	$628.90	$628.90