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	$128.50	8.512%	$139.4379	$139.44	$139.45	$139.40
Purchase #2	$22.37	13.832%	$25.4642	$25.46	$25.45	$25.50
Purchase #3	$213.64	8.820%	$232.483	$232.48	$232.50	$232.50
Purchase #4	$111.59	6.786%	$119.1625	$119.16	$119.15	$119.20
Purchase #5	$205.46	13.703%	$233.6142	$233.61	$233.60	$233.60
Purchase #6	$139.28	4.617%	$145.7106	$145.71	$145.70	$145.70
Purchase #7	$182.84	7.375%	$196.3245	$196.32	$196.30	$196.30
7 purchase totals =	$1,003.68		$1,092.1969	$1,092.18	$1,092.15	$1,092.20