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	$93.61	10.574%	$103.5083	$103.51	$103.50	$103.50
Purchase #2	$162.67	3.854%	$168.9393	$168.94	$168.95	$168.90
Purchase #3	$51.47	7.155%	$55.1527	$55.15	$55.15	$55.20
Purchase #4	$26.69	8.229%	$28.8863	$28.89	$28.90	$28.90
Purchase #5	$6.92	9.815%	$7.5992	$7.60	$7.60	$7.60
Purchase #6	$23.78	3.402%	$24.589	$24.59	$24.60	$24.60
Purchase #7	$105.87	4.643%	$110.7855	$110.79	$110.80	$110.80
7 purchase totals =	$471.01		$499.4603	$499.47	$499.50	$499.50