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	$229.32	7.315%	$246.0948	$246.09	$246.10	$246.10
Purchase #2	$104.54	4.756%	$109.5119	$109.51	$109.50	$109.50
Purchase #3	$240.30	7.205%	$257.6136	$257.61	$257.60	$257.60
Purchase #4	$20.59	4.817%	$21.5818	$21.58	$21.60	$21.60
Purchase #5	$86.28	4.769%	$90.3947	$90.39	$90.40	$90.40
Purchase #6	$148.69	11.841%	$166.2964	$166.30	$166.30	$166.30
Purchase #7	$22.58	13.683%	$25.6696	$25.67	$25.65	$25.70
7 purchase totals =	$852.30		$917.1628	$917.15	$917.15	$917.20