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	$218.93	10.724%	$242.4081	$242.41	$242.40	$242.40
Purchase #2	$115.61	11.685%	$129.119	$129.12	$129.10	$129.10
Purchase #3	$69.54	9.815%	$76.3654	$76.37	$76.35	$76.40
Purchase #4	$241.89	3.539%	$250.4505	$250.45	$250.45	$250.50
Purchase #5	$51.68	3.141%	$53.3033	$53.30	$53.30	$53.30
Purchase #6	$81.88	11.259%	$91.0989	$91.10	$91.10	$91.10
Purchase #7	$51.25	12.330%	$57.5691	$57.57	$57.55	$57.60
7 purchase totals =	$830.78		$900.3143	$900.32	$900.25	$900.40