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	$9.63	3.375%	$9.955	$9.96	$9.95	$10.00
Purchase #2	$236.71	8.683%	$257.2635	$257.26	$257.25	$257.30
Purchase #3	$201.61	10.295%	$222.3657	$222.37	$222.35	$222.40
Purchase #4	$55.94	7.111%	$59.9179	$59.92	$59.90	$59.90
Purchase #5	$154.87	8.822%	$168.5326	$168.53	$168.55	$168.50
Purchase #6	$86.41	6.400%	$91.9402	$91.94	$91.95	$91.90
Purchase #7	$145.90	13.816%	$166.0575	$166.06	$166.05	$166.10
7 purchase totals =	$891.07		$976.0324	$976.04	$976.00	$976.10