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	$227.29	12.784%	$256.3468	$256.35	$256.35	$256.30
Purchase #2	$233.96	8.526%	$253.9074	$253.91	$253.90	$253.90
Purchase #3	$52.67	9.861%	$57.8638	$57.86	$57.85	$57.90
Purchase #4	$235.67	3.259%	$243.3505	$243.35	$243.35	$243.40
Purchase #5	$141.31	11.732%	$157.8885	$157.89	$157.90	$157.90
Purchase #6	$54.31	6.308%	$57.7359	$57.74	$57.75	$57.70
Purchase #7	$148.41	9.392%	$162.3487	$162.35	$162.35	$162.30
7 purchase totals =	$1,093.62		$1,189.4416	$1,189.45	$1,189.45	$1,189.40