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	$134.74	5.264%	$141.8327	$141.83	$141.85	$141.80
Purchase #2	$36.42	6.848%	$38.914	$38.91	$38.90	$38.90
Purchase #3	$137.48	8.333%	$148.9362	$148.94	$148.95	$148.90
Purchase #4	$241.92	3.248%	$249.7776	$249.78	$249.80	$249.80
Purchase #5	$85.27	12.390%	$95.835	$95.84	$95.85	$95.80
Purchase #6	$75.51	8.692%	$82.0733	$82.07	$82.05	$82.10
Purchase #7	$90.77	3.433%	$93.8861	$93.89	$93.90	$93.90
7 purchase totals =	$802.11		$851.2549	$851.26	$851.30	$851.20