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	$211.91	13.216%	$239.916	$239.92	$239.90	$239.90
Purchase #2	$82.77	10.859%	$91.758	$91.76	$91.75	$91.80
Purchase #3	$140.45	7.201%	$150.5638	$150.56	$150.55	$150.60
Purchase #4	$210.38	3.576%	$217.9032	$217.90	$217.90	$217.90
Purchase #5	$105.75	10.367%	$116.7131	$116.71	$116.70	$116.70
Purchase #6	$181.31	9.831%	$199.1346	$199.13	$199.15	$199.10
Purchase #7	$32.75	9.701%	$35.9271	$35.93	$35.95	$35.90
7 purchase totals =	$965.32		$1,051.9158	$1,051.91	$1,051.90	$1,051.90