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	$89.84	10.629%	$99.3891	$99.39	$99.40	$99.40
Purchase #2	$88.88	6.314%	$94.4919	$94.49	$94.50	$94.50
Purchase #3	$35.28	12.277%	$39.6113	$39.61	$39.60	$39.60
Purchase #4	$198.47	10.133%	$218.581	$218.58	$218.60	$218.60
Purchase #5	$55.90	4.315%	$58.3121	$58.31	$58.30	$58.30
Purchase #6	$143.79	8.150%	$155.5089	$155.51	$155.50	$155.50
Purchase #7	$31.96	5.276%	$33.6462	$33.65	$33.65	$33.60
7 purchase totals =	$644.12		$699.5405	$699.54	$699.55	$699.50