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	$96.88	7.616%	$104.2584	$104.26	$104.25	$104.30
Purchase #2	$139.34	4.376%	$145.4375	$145.44	$145.45	$145.40
Purchase #3	$112.84	6.803%	$120.5165	$120.52	$120.50	$120.50
Purchase #4	$54.86	11.817%	$61.3428	$61.34	$61.35	$61.30
Purchase #5	$219.81	6.870%	$234.9109	$234.91	$234.90	$234.90
Purchase #6	$51.77	3.564%	$53.6151	$53.62	$53.60	$53.60
Purchase #7	$78.92	3.302%	$81.5259	$81.53	$81.55	$81.50
7 purchase totals =	$754.42		$801.6071	$801.62	$801.60	$801.50