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	$68.43	13.873%	$77.9233	$77.92	$77.90	$77.90
Purchase #2	$56.70	9.204%	$61.9187	$61.92	$61.90	$61.90
Purchase #3	$215.49	6.518%	$229.5356	$229.54	$229.55	$229.50
Purchase #4	$20.89	3.143%	$21.5466	$21.55	$21.55	$21.50
Purchase #5	$180.94	5.123%	$190.2096	$190.21	$190.20	$190.20
Purchase #6	$32.35	3.691%	$33.544	$33.54	$33.55	$33.50
Purchase #7	$166.87	6.835%	$178.2756	$178.28	$178.30	$178.30
7 purchase totals =	$741.67		$792.9534	$792.96	$792.95	$792.80