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	$164.59	13.561%	$186.91	$186.91	$186.90	$186.90
Purchase #2	$103.91	5.227%	$109.3414	$109.34	$109.35	$109.30
Purchase #3	$207.93	11.410%	$231.6548	$231.65	$231.65	$231.70
Purchase #4	$185.54	4.282%	$193.4848	$193.48	$193.50	$193.50
Purchase #5	$171.88	5.237%	$180.8814	$180.88	$180.90	$180.90
Purchase #6	$243.31	10.655%	$269.2347	$269.23	$269.25	$269.20
Purchase #7	$35.87	11.606%	$40.0331	$40.03	$40.05	$40.00
7 purchase totals =	$1,113.03		$1,211.5402	$1,211.52	$1,211.60	$1,211.50