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	$82.36	8.158%	$89.0789	$89.08	$89.10	$89.10
Purchase #2	$240.27	13.761%	$273.3336	$273.33	$273.35	$273.30
Purchase #3	$134.92	11.164%	$149.9825	$149.98	$150.00	$150.00
Purchase #4	$219.51	6.833%	$234.5091	$234.51	$234.50	$234.50
Purchase #5	$243.97	11.718%	$272.5584	$272.56	$272.55	$272.60
Purchase #6	$165.61	11.742%	$185.0559	$185.06	$185.05	$185.10
Purchase #7	$150.73	9.418%	$164.9258	$164.93	$164.95	$164.90
7 purchase totals =	$1,237.37		$1,369.4442	$1,369.45	$1,369.50	$1,369.50