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	$231.69	11.122%	$257.4586	$257.46	$257.45	$257.50
Purchase #2	$78.40	6.222%	$83.278	$83.28	$83.30	$83.30
Purchase #3	$126.61	7.170%	$135.6879	$135.69	$135.70	$135.70
Purchase #4	$32.88	13.731%	$37.3948	$37.39	$37.40	$37.40
Purchase #5	$72.32	13.425%	$82.029	$82.03	$82.05	$82.00
Purchase #6	$79.58	9.173%	$86.8799	$86.88	$86.90	$86.90
Purchase #7	$200.88	6.770%	$214.4796	$214.48	$214.50	$214.50
7 purchase totals =	$822.36		$897.2078	$897.21	$897.30	$897.30