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	$108.70	13.787%	$123.6865	$123.69	$123.70	$123.70
Purchase #2	$82.52	7.179%	$88.4441	$88.44	$88.45	$88.40
Purchase #3	$64.61	12.573%	$72.7334	$72.73	$72.75	$72.70
Purchase #4	$87.50	10.790%	$96.9413	$96.94	$96.95	$96.90
Purchase #5	$13.77	6.786%	$14.7044	$14.70	$14.70	$14.70
Purchase #6	$151.74	5.301%	$159.7837	$159.78	$159.80	$159.80
Purchase #7	$83.69	8.706%	$90.9761	$90.98	$91.00	$91.00
7 purchase totals =	$592.53		$647.2695	$647.26	$647.35	$647.20