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	$52.85	5.340%	$55.6722	$55.67	$55.65	$55.70
Purchase #2	$173.44	8.532%	$188.2379	$188.24	$188.25	$188.20
Purchase #3	$215.87	9.678%	$236.7619	$236.76	$236.75	$236.80
Purchase #4	$141.62	6.112%	$150.2758	$150.28	$150.30	$150.30
Purchase #5	$171.76	12.293%	$192.8745	$192.87	$192.85	$192.90
Purchase #6	$152.89	10.436%	$168.8456	$168.85	$168.85	$168.80
Purchase #7	$18.29	3.299%	$18.8934	$18.89	$18.90	$18.90
7 purchase totals =	$926.72		$1,011.5613	$1,011.56	$1,011.55	$1,011.60