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	$122.29	4.801%	$128.1611	$128.16	$128.15	$128.20
Purchase #2	$99.81	9.419%	$109.2111	$109.21	$109.20	$109.20
Purchase #3	$28.33	8.443%	$30.7219	$30.72	$30.70	$30.70
Purchase #4	$22.34	7.528%	$24.0218	$24.02	$24.00	$24.00
Purchase #5	$149.60	6.212%	$158.8932	$158.89	$158.90	$158.90
Purchase #6	$246.79	10.624%	$273.009	$273.01	$273.00	$273.00
Purchase #7	$169.39	13.277%	$191.8799	$191.88	$191.90	$191.90
7 purchase totals =	$838.55		$915.8980	$915.89	$915.85	$915.90