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	$5.37	12.219%	$6.0262	$6.03	$6.05	$6.00
Purchase #2	$150.38	5.321%	$158.3817	$158.38	$158.40	$158.40
Purchase #3	$161.90	11.270%	$180.1461	$180.15	$180.15	$180.10
Purchase #4	$155.30	3.393%	$160.5693	$160.57	$160.55	$160.60
Purchase #5	$209.41	13.653%	$238.0007	$238.00	$238.00	$238.00
Purchase #6	$231.88	10.470%	$256.1578	$256.16	$256.15	$256.20
Purchase #7	$58.63	3.360%	$60.6	$60.60	$60.60	$60.60
7 purchase totals =	$972.87		$1,059.8818	$1,059.89	$1,059.90	$1,059.90