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	$101.52	13.560%	$115.2861	$115.29	$115.30	$115.30
Purchase #2	$182.38	7.520%	$196.095	$196.10	$196.10	$196.10
Purchase #3	$64.73	10.188%	$71.3247	$71.32	$71.30	$71.30
Purchase #4	$9.33	9.256%	$10.1936	$10.19	$10.20	$10.20
Purchase #5	$5.81	8.693%	$6.3151	$6.32	$6.30	$6.30
Purchase #6	$27.49	13.822%	$31.2897	$31.29	$31.30	$31.30
Purchase #7	$116.26	10.182%	$128.0976	$128.10	$128.10	$128.10
7 purchase totals =	$507.52		$558.6018	$558.61	$558.60	$558.60