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	$38.58	9.709%	$42.3257	$42.33	$42.35	$42.30
Purchase #2	$78.73	4.311%	$82.1241	$82.12	$82.10	$82.10
Purchase #3	$90.59	13.775%	$103.0688	$103.07	$103.05	$103.10
Purchase #4	$78.46	12.272%	$88.0886	$88.09	$88.10	$88.10
Purchase #5	$47.71	9.265%	$52.1303	$52.13	$52.15	$52.10
Purchase #6	$162.50	4.698%	$170.1343	$170.13	$170.15	$170.10
Purchase #7	$72.61	8.421%	$78.7245	$78.72	$78.70	$78.70
7 purchase totals =	$569.18		$616.5963	$616.59	$616.60	$616.50