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	$82.74	9.405%	$90.5217	$90.52	$90.50	$90.50
Purchase #2	$167.35	10.164%	$184.3595	$184.36	$184.35	$184.40
Purchase #3	$119.53	7.835%	$128.8952	$128.90	$128.90	$128.90
Purchase #4	$69.91	3.294%	$72.2128	$72.21	$72.20	$72.20
Purchase #5	$92.93	3.372%	$96.0636	$96.06	$96.05	$96.10
Purchase #6	$151.60	13.701%	$172.3707	$172.37	$172.35	$172.40
Purchase #7	$222.72	6.214%	$236.5598	$236.56	$236.55	$236.60
7 purchase totals =	$906.78		$980.9833	$980.98	$980.90	$981.10