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	$205.79	7.145%	$220.4937	$220.49	$220.50	$220.50
Purchase #2	$110.59	12.280%	$124.1705	$124.17	$124.15	$124.20
Purchase #3	$90.43	9.764%	$99.2596	$99.26	$99.25	$99.30
Purchase #4	$229.80	3.458%	$237.7465	$237.75	$237.75	$237.70
Purchase #5	$176.51	4.544%	$184.5306	$184.53	$184.55	$184.50
Purchase #6	$31.51	6.256%	$33.4813	$33.48	$33.50	$33.50
Purchase #7	$162.67	5.689%	$171.9243	$171.92	$171.90	$171.90
7 purchase totals =	$1,007.30		$1,071.6065	$1,071.60	$1,071.60	$1,071.60