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	$241.54	13.343%	$273.7687	$273.77	$273.75	$273.80
Purchase #2	$236.35	8.296%	$255.9576	$255.96	$255.95	$256.00
Purchase #3	$30.48	6.854%	$32.5691	$32.57	$32.55	$32.60
Purchase #4	$144.48	7.556%	$155.3969	$155.40	$155.40	$155.40
Purchase #5	$123.55	11.647%	$137.9399	$137.94	$137.95	$137.90
Purchase #6	$35.77	8.782%	$38.9113	$38.91	$38.90	$38.90
Purchase #7	$34.85	8.712%	$37.8861	$37.89	$37.90	$37.90
7 purchase totals =	$847.02		$932.4296	$932.44	$932.40	$932.50