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	$152.42	10.408%	$168.2839	$168.28	$168.30	$168.30
Purchase #2	$12.62	7.515%	$13.5684	$13.57	$13.55	$13.60
Purchase #3	$107.50	10.779%	$119.0874	$119.09	$119.10	$119.10
Purchase #4	$117.62	5.557%	$124.1561	$124.16	$124.15	$124.20
Purchase #5	$59.82	13.216%	$67.7258	$67.73	$67.75	$67.70
Purchase #6	$96.33	9.863%	$105.831	$105.83	$105.85	$105.80
Purchase #7	$36.79	3.808%	$38.191	$38.19	$38.20	$38.20
7 purchase totals =	$583.10		$636.8436	$636.85	$636.90	$636.90