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	$119.72	3.201%	$123.5522	$123.55	$123.55	$123.60
Purchase #2	$52.71	8.119%	$56.9895	$56.99	$57.00	$57.00
Purchase #3	$183.88	6.475%	$195.7862	$195.79	$195.80	$195.80
Purchase #4	$72.98	12.495%	$82.0989	$82.10	$82.10	$82.10
Purchase #5	$137.94	10.494%	$152.4154	$152.42	$152.40	$152.40
Purchase #6	$37.74	11.650%	$42.1367	$42.14	$42.15	$42.10
Purchase #7	$97.63	9.669%	$107.0698	$107.07	$107.05	$107.10
7 purchase totals =	$702.60		$760.0487	$760.06	$760.05	$760.10