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	$97.93	12.213%	$109.8902	$109.89	$109.90	$109.90
Purchase #2	$107.25	11.565%	$119.6535	$119.65	$119.65	$119.70
Purchase #3	$55.60	10.744%	$61.5737	$61.57	$61.55	$61.60
Purchase #4	$209.89	3.658%	$217.5678	$217.57	$217.55	$217.60
Purchase #5	$210.26	3.736%	$218.1153	$218.12	$218.10	$218.10
Purchase #6	$28.57	12.606%	$32.1715	$32.17	$32.15	$32.20
Purchase #7	$235.38	11.652%	$262.8065	$262.81	$262.80	$262.80
7 purchase totals =	$944.88		$1,021.7785	$1,021.78	$1,021.70	$1,021.90