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	$150.42	8.175%	$162.7168	$162.72	$162.70	$162.70
Purchase #2	$104.92	3.461%	$108.5513	$108.55	$108.55	$108.60
Purchase #3	$77.43	11.506%	$86.3391	$86.34	$86.35	$86.30
Purchase #4	$39.92	6.647%	$42.5735	$42.57	$42.55	$42.60
Purchase #5	$59.91	13.830%	$68.1956	$68.20	$68.20	$68.20
Purchase #6	$166.58	4.755%	$174.5009	$174.50	$174.50	$174.50
Purchase #7	$181.71	10.266%	$200.3643	$200.36	$200.35	$200.40
7 purchase totals =	$780.89		$843.2415	$843.24	$843.20	$843.30