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	$129.72	3.541%	$134.3134	$134.31	$134.30	$134.30
Purchase #2	$168.89	7.473%	$181.5111	$181.51	$181.50	$181.50
Purchase #3	$85.51	9.695%	$93.8002	$93.80	$93.80	$93.80
Purchase #4	$160.86	6.485%	$171.2918	$171.29	$171.30	$171.30
Purchase #5	$72.71	8.650%	$78.9994	$79.00	$79.00	$79.00
Purchase #6	$68.89	5.655%	$72.7857	$72.79	$72.80	$72.80
Purchase #7	$38.32	11.749%	$42.8222	$42.82	$42.80	$42.80
7 purchase totals =	$724.90		$775.5238	$775.52	$775.50	$775.50