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	$81.40	11.847%	$91.0435	$91.04	$91.05	$91.00
Purchase #2	$220.78	6.524%	$235.1837	$235.18	$235.20	$235.20
Purchase #3	$175.80	11.789%	$196.5251	$196.53	$196.55	$196.50
Purchase #4	$229.36	5.330%	$241.5849	$241.58	$241.60	$241.60
Purchase #5	$104.38	8.807%	$113.5727	$113.57	$113.55	$113.60
Purchase #6	$65.82	4.697%	$68.9116	$68.91	$68.90	$68.90
Purchase #7	$169.83	6.850%	$181.4634	$181.46	$181.45	$181.50
7 purchase totals =	$1,047.37		$1,128.2849	$1,128.27	$1,128.30	$1,128.30