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	$182.42	4.380%	$190.41	$190.41	$190.40	$190.40
Purchase #2	$82.51	10.633%	$91.2833	$91.28	$91.30	$91.30
Purchase #3	$248.32	13.632%	$282.171	$282.17	$282.15	$282.20
Purchase #4	$131.54	12.491%	$147.9707	$147.97	$147.95	$148.00
Purchase #5	$192.32	13.453%	$218.1928	$218.19	$218.20	$218.20
Purchase #6	$157.35	7.336%	$168.8932	$168.89	$168.90	$168.90
Purchase #7	$167.32	13.782%	$190.38	$190.38	$190.40	$190.40
7 purchase totals =	$1,161.78		$1,289.3010	$1,289.29	$1,289.30	$1,289.40