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	$9.92	5.701%	$10.4855	$10.49	$10.50	$10.50
Purchase #2	$194.90	10.229%	$214.8363	$214.84	$214.85	$214.80
Purchase #3	$113.59	5.515%	$119.8545	$119.85	$119.85	$119.90
Purchase #4	$83.40	13.281%	$94.4764	$94.48	$94.50	$94.50
Purchase #5	$6.50	13.700%	$7.3905	$7.39	$7.40	$7.40
Purchase #6	$14.26	10.170%	$15.7102	$15.71	$15.70	$15.70
Purchase #7	$75.33	4.177%	$78.4765	$78.48	$78.50	$78.50
7 purchase totals =	$497.90		$541.2299	$541.24	$541.30	$541.30