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	$99.90	3.513%	$103.4095	$103.41	$103.40	$103.40
Purchase #2	$167.30	12.274%	$187.8344	$187.83	$187.85	$187.80
Purchase #3	$82.84	4.426%	$86.5065	$86.51	$86.50	$86.50
Purchase #4	$111.35	10.804%	$123.3803	$123.38	$123.40	$123.40
Purchase #5	$147.40	12.585%	$165.9503	$165.95	$165.95	$166.00
Purchase #6	$92.95	3.672%	$96.3631	$96.36	$96.35	$96.40
Purchase #7	$111.55	7.206%	$119.5883	$119.59	$119.60	$119.60
7 purchase totals =	$813.29		$883.0324	$883.03	$883.05	$883.10