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	$92.48	12.497%	$104.0372	$104.04	$104.05	$104.00
Purchase #2	$104.53	6.770%	$111.6067	$111.61	$111.60	$111.60
Purchase #3	$85.29	3.308%	$88.1114	$88.11	$88.10	$88.10
Purchase #4	$92.77	11.240%	$103.1973	$103.20	$103.20	$103.20
Purchase #5	$158.59	9.792%	$174.1191	$174.12	$174.10	$174.10
Purchase #6	$177.69	6.486%	$189.215	$189.22	$189.20	$189.20
Purchase #7	$52.48	10.329%	$57.9007	$57.90	$57.90	$57.90
7 purchase totals =	$763.83		$828.1874	$828.20	$828.15	$828.10