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	$109.51	5.213%	$115.2188	$115.22	$115.20	$115.20
Purchase #2	$213.47	13.378%	$242.028	$242.03	$242.05	$242.00
Purchase #3	$24.77	12.589%	$27.8883	$27.89	$27.90	$27.90
Purchase #4	$213.46	13.150%	$241.53	$241.53	$241.55	$241.50
Purchase #5	$249.71	3.502%	$258.4548	$258.45	$258.45	$258.50
Purchase #6	$142.31	7.477%	$152.9505	$152.95	$152.95	$153.00
Purchase #7	$97.74	7.661%	$105.2279	$105.23	$105.25	$105.20
7 purchase totals =	$1,050.97		$1,143.2983	$1,143.30	$1,143.35	$1,143.30