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	$101.85	7.522%	$109.5112	$109.51	$109.50	$109.50
Purchase #2	$119.47	10.770%	$132.3369	$132.34	$132.35	$132.30
Purchase #3	$146.54	10.686%	$162.1993	$162.20	$162.20	$162.20
Purchase #4	$215.90	13.660%	$245.3919	$245.39	$245.40	$245.40
Purchase #5	$243.35	10.150%	$268.05	$268.05	$268.05	$268.10
Purchase #6	$30.88	3.238%	$31.8799	$31.88	$31.90	$31.90
Purchase #7	$142.79	4.765%	$149.5939	$149.59	$149.60	$149.60
7 purchase totals =	$1,000.78		$1,098.9631	$1,098.96	$1,099.00	$1,099.00