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	$224.98	10.212%	$247.955	$247.96	$247.95	$248.00
Purchase #2	$135.69	12.673%	$152.886	$152.89	$152.90	$152.90
Purchase #3	$152.76	6.635%	$162.8956	$162.90	$162.90	$162.90
Purchase #4	$180.86	10.471%	$199.7979	$199.80	$199.80	$199.80
Purchase #5	$148.55	13.368%	$168.4082	$168.41	$168.40	$168.40
Purchase #6	$111.49	7.184%	$119.4994	$119.50	$119.50	$119.50
Purchase #7	$36.45	5.691%	$38.5244	$38.52	$38.50	$38.50
7 purchase totals =	$990.78		$1,089.9665	$1,089.98	$1,089.95	$1,090.00