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	$220.27	7.735%	$237.3079	$237.31	$237.30	$237.30
Purchase #2	$232.85	12.141%	$261.1203	$261.12	$261.10	$261.10
Purchase #3	$101.97	13.152%	$115.3811	$115.38	$115.40	$115.40
Purchase #4	$137.98	10.504%	$152.4734	$152.47	$152.45	$152.50
Purchase #5	$56.94	4.661%	$59.594	$59.59	$59.60	$59.60
Purchase #6	$23.38	10.700%	$25.8817	$25.88	$25.90	$25.90
Purchase #7	$212.81	10.255%	$234.6337	$234.63	$234.65	$234.60
7 purchase totals =	$986.20		$1,086.3921	$1,086.38	$1,086.40	$1,086.40