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	$51.40	9.867%	$56.4716	$56.47	$56.45	$56.50
Purchase #2	$104.57	11.296%	$116.3822	$116.38	$116.40	$116.40
Purchase #3	$210.86	11.336%	$234.7631	$234.76	$234.75	$234.80
Purchase #4	$213.57	7.449%	$229.4788	$229.48	$229.50	$229.50
Purchase #5	$237.31	5.362%	$250.0346	$250.03	$250.05	$250.00
Purchase #6	$60.61	10.750%	$67.1256	$67.13	$67.15	$67.10
Purchase #7	$178.79	5.549%	$188.7111	$188.71	$188.70	$188.70
7 purchase totals =	$1,057.11		$1,142.9670	$1,142.96	$1,143.00	$1,143.00