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	$40.70	13.559%	$46.2185	$46.22	$46.20	$46.20
Purchase #2	$110.80	13.179%	$125.4023	$125.40	$125.40	$125.40
Purchase #3	$37.93	10.238%	$41.8133	$41.81	$41.80	$41.80
Purchase #4	$205.30	8.555%	$222.8634	$222.86	$222.85	$222.90
Purchase #5	$33.96	4.666%	$35.5446	$35.54	$35.55	$35.50
Purchase #6	$99.96	8.582%	$108.5386	$108.54	$108.55	$108.50
Purchase #7	$224.44	13.588%	$254.9369	$254.94	$254.95	$254.90
7 purchase totals =	$753.09		$835.3176	$835.31	$835.30	$835.20