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	$85.93	3.673%	$89.0862	$89.09	$89.10	$89.10
Purchase #2	$73.33	9.813%	$80.5259	$80.53	$80.55	$80.50
Purchase #3	$23.93	8.228%	$25.899	$25.90	$25.90	$25.90
Purchase #4	$95.74	7.118%	$102.5548	$102.55	$102.55	$102.60
Purchase #5	$134.60	9.137%	$146.8984	$146.90	$146.90	$146.90
Purchase #6	$165.88	3.687%	$171.996	$172.00	$172.00	$172.00
Purchase #7	$199.37	13.522%	$226.3288	$226.33	$226.35	$226.30
7 purchase totals =	$778.78		$843.2891	$843.30	$843.35	$843.30