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	$31.86	12.712%	$35.91	$35.91	$35.90	$35.90
Purchase #2	$86.33	3.454%	$89.3118	$89.31	$89.30	$89.30
Purchase #3	$92.94	4.375%	$97.0061	$97.01	$97.00	$97.00
Purchase #4	$119.58	6.336%	$127.1566	$127.16	$127.15	$127.20
Purchase #5	$103.42	7.181%	$110.8466	$110.85	$110.85	$110.80
Purchase #6	$96.71	8.432%	$104.8646	$104.86	$104.85	$104.90
Purchase #7	$21.65	8.550%	$23.5011	$23.50	$23.50	$23.50
7 purchase totals =	$552.49		$588.5968	$588.60	$588.55	$588.60