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	$16.37	12.732%	$18.4542	$18.45	$18.45	$18.50
Purchase #2	$223.57	3.262%	$230.8629	$230.86	$230.85	$230.90
Purchase #3	$136.54	7.505%	$146.7873	$146.79	$146.80	$146.80
Purchase #4	$198.55	12.705%	$223.7758	$223.78	$223.80	$223.80
Purchase #5	$198.78	3.401%	$205.5405	$205.54	$205.55	$205.50
Purchase #6	$191.58	3.828%	$198.9137	$198.91	$198.90	$198.90
Purchase #7	$85.33	12.122%	$95.6737	$95.67	$95.65	$95.70
7 purchase totals =	$1,050.72		$1,120.0081	$1,120.00	$1,120.00	$1,120.10