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	$30.48	4.639%	$31.894	$31.89	$31.90	$31.90
Purchase #2	$204.27	9.794%	$224.2762	$224.28	$224.30	$224.30
Purchase #3	$163.33	13.468%	$185.3273	$185.33	$185.35	$185.30
Purchase #4	$159.62	12.850%	$180.1312	$180.13	$180.15	$180.10
Purchase #5	$183.29	9.466%	$200.6402	$200.64	$200.65	$200.60
Purchase #6	$166.38	8.387%	$180.3343	$180.33	$180.35	$180.30
Purchase #7	$54.79	5.618%	$57.8681	$57.87	$57.85	$57.90
7 purchase totals =	$962.16		$1,060.4713	$1,060.47	$1,060.55	$1,060.40